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. 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 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 Due within One Year, Amortized Cost Scanner Appliances [Member] Represents information related to scanner appliances. Hedging Relationship [Domain] Note 3 - Accumulated Other Comprehensive Income (Loss) 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. Note 6 - Intangible Assets, Net Not Designated as Hedging Instrument [Member] Note 7 - Leases Due after One Year through Two Years Represents fair value of debt maturities for available-for-sale securities through year one to year two. Note 9 - Stockholders' Equity and Stock-based Compensation Note 10 - Net Income Per Share Net change in unrealized gains (losses) on available-for-sale debt securities, net of tax Mature over Two Years Represents fair value of available-for-sale for debt maturities after year two. Hedging Relationship [Axis] Income Tax Disclosure [Text Block] Note 12 - Segment Information and Information About Geographic Area Accumulated Other Comprehensive Income Disclosure [Text Block] The entire note disclosure of accumulated other comprehensive income. Note 2 - Fair Value of Financial Instruments - Fair Value Hierarchy (Details) Hedging Designation [Axis] Note 2 - Fair Value of Financial Instruments - Cash and Cash Equivalents (Details) Hedging Designation [Domain] Note 2 - Fair Value of Financial Instruments - Summary of Securities in Unrealized Loss Positions (Details) Designated as Hedging Instrument [Member] us-gaap_LiabilitiesCurrent Total current liabilities Note 2 - Fair Value of Financial Instruments - Summary of the Fair Value of Marketable Securities (Details) Due within One Year Represents fair value of available-for-sale securities for debt maturities for next twelve months. Note 2 - Fair Value of Financial Instruments - Summary of Derivative Financial Instruments (Details) 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) Due after One Year through Two Years, Amortized Cost Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after year one through year two. Asset-Backed Securities [Member] Note 3 - Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from AOCI (Details) Note 4 - Property and Equipment, Net - Property and Equipment, Net (Details) Note 5 - Revenue from Contracts with Customers - Expected Revenue from All Remaining Performance Obligations (Details) Note 5 - Revenue from Contracts with Customers - Expected Revenue from All Remaining Performance Obligations 2 (Details) Note 5 - Revenue From Contracts With Customers - Revenue by Sales Channel (Details) Note 5 - Revenue From Contracts With Customers - Capitalized Cost to Obtain Contracts, Current and Noncurrent (Details) qlys_SharebasedCompensationTerminationPeriodTrigger Share-based Compensation Termination Period Trigger (Month) Represents termination period trigger for share-based compensation. Note 6 - Intangible Assets, Net - Carrying Value of Intangible Assets (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 6 - Intangible Assets, Net - Expected Amortization Expense in Future Periods (Details) Note 7 - Leases - Supplemental Cash Flow Information (Details) Note 7 - Leases - Weighted Average Remaining Lease Term and Weighted Average Discount Rate (Details) Mature over Two Years, Amortized Cost Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after second fiscal year following current fiscal year. Note 9 - Stockholders' Equity and Stock-based Compensation - Summary of Stock-based Compensation Expense (Details) Share-Based Payment Arrangement, Option, Activity [Table Text Block] Note 9 - Stockholders' Equity and Stock-based Compensation - Share-based Compensation and Stock Options Activity (Details) Assembled Workforce [Member] Represents Assembled Workforce. Note 9 - Stockholders' Equity and Stock-based Compensation - Share-based Compensation, Restricted Stock and Restricted Stock Units (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. us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue Granted, weighted average grant date fair value (in dollars per share) Note 9 - Stockholders' Equity and Stock-based Compensation - Schedule of Repurchase Agreements (Details) us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss 12 Months or Longer, Accumulated Loss Vested, weighted average grant date fair value (in dollars per share) Sales and maturities of marketable securities us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss Unrealized Loss Position, accumulated loss Note 10 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) Forfeited, weighted average grant date fair value (in dollars per share) Note 10 - Net Income Per Share - Anti-dilutive Net Income Per Share (Details) Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] 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 12 - Segment Information and Information About Geographic Area - Revenue and Property and Equipment, Net by Geographic Area (Details) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Forfeited, number of shares (in shares) Notes To Financial Statements Notes To Financial Statements [Abstract] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Balance, number of shares (in shares) Balance, number of shares (in shares) Commercial Paper, Not Included with Cash and Cash Equivalents [Member] Other foreign currency transactions losses us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss Less than 12 Months, Accumulated Loss Schedule of Derivative Instruments [Table Text Block] Exercisable, weighted average remaining contractual life (Year) US Government Corporations and Agencies Securities [Member] qlys_CashEquivalentsUnrealizedLoss cash equivalents, unrealized loss cash equivalents, unrealized loss The amount of unrealized loss from cash equivalents. US Government Agencies Debt Securities [Member] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested, number of shares (in shares) Corporate Debt Securities [Member] 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) Exercisable (in shares) Weighted average exercise price, Exercisable (in dollars per share) qlys_CashEquivalentsUnrealizedGains Cash equivalents unrealized gains Represents accumulated gross unrealized gain of cash equivalents. Exercisable, aggregate intrinsic value qlys_CashEquivalentsFairValueDisclosure Cash equivalent, fair value Fair value portion of cash equivalent. Vested and expected to vest (in shares) Weighted average exercise price, Vested and expected to vest (in dollars per share) Vested and Expected to vest, aggregate intrinsic value Foreign Exchange Contract [Member] Unrealized Loss Position, fair value Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] Weighted Average Remaining Contractual Life Balance (Year) Aggregate intrinsic value Less than 12 Months, fair value 12 Months or Longer, fair value 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. Deferred revenues, current Accrued liabilities and other noncurrent liabilities increase(decrease) in accrued liabilities and other noncurrent liabilities. 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) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod Canceled (in shares) 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) 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_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) 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] Current liabilities: Vesting [Axis] Developed Technology Rights [Member] Additional Authorized Dollar Value Amount of additional stock repurchase plan authorized 1. Vesting [Domain] us-gaap_Assets Total assets Patents [Member] Plan Name [Axis] Shareholders' Equity and Share-Based Payments [Text Block] Plan Name [Domain] us-gaap_OperatingLeaseExpense Operating Lease, Expense us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1 Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) 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 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] us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Less: accumulated depreciation and amortization Property and equipment, net Property, Plant and Equipment, Net Property and equipment and finance lease, net Goodwill us-gaap_PropertyPlantAndEquipmentGross Property and equipment and finance lease Net gains from non-designated forward contracts us-gaap_Investments Investments Derivative Instrument [Axis] Derivative Contract [Domain] Cash flow from investing activities: Available-for-Sale, Total Net income per share: Earnings Per Share [Text Block] us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments Total Income tax provision Income Tax Expense (Benefit) 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. Employee Stock Purchase Plan Shares [Member] Represents information regarding employee stock purchase plan shares. us-gaap_OperatingExpenses Total operating expenses Restricted cash General and administrative us-gaap_Cash Cash cash equivalents, amortized cost cash equivalents, amortized cost Cash and cash equivalents 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 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] us-gaap_FinancialInstrumentsOwnedAtFairValue Total assets New Accounting Pronouncements, Policy [Policy Text Block] Foreign currency forward contracts 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) 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 Filer Category Entity Current Reporting Status 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] Legal Entity [Axis] Entity Address, Address Line One Issuance of common stock through employee stock purchase plan us-gaap_AmortizationOfIntangibleAssets Amortization of Intangible Assets 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 Investments [Domain] Trading Symbol Investment Type [Axis] Issuance of common stock through employee stock purchase plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares) Local Phone Number Issuance of common stock upon exercise of stock options (in shares) Exercised (in shares) us-gaap_TableTextBlock Notes Tables Issuance of common stock upon exercise of stock options Provision for credit losses us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross Granted (in shares) Sales and marketing us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and stockholders’ equity UNITED STATES Accumulated deficit Research and development Accumulated other comprehensive loss Money Market Funds [Member] Cash and Cash Equivalents [Axis] Derivative Instruments, Gain (Loss) [Table Text Block] Cash and Cash Equivalents [Domain] Changes in operating assets and liabilities: us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Operating lease liabilities, noncurrent Deferred income taxes Operating lease liabilities, current Operating leases - right of use asset us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear 2023 (remaining nine months) us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo 2025 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree 2026 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour 2027 Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths 2024 Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block] Noncurrent Other noncurrent assets us-gaap_ShareBasedCompensation Stock-based compensation Weighted Average Remaining Life (Year) Weighted Average Life (Year) Operating expenses: us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments Amortization (accretion) of premiums (discount) on marketable securities, net 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_FinancialLiabilitiesFairValueDisclosure Total liabilities us-gaap_ForeignCurrencyContractAssetFairValueDisclosure Foreign currency forward contracts us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure Foreign currency forward contracts Foreign currency forward contracts us-gaap_AssetsCurrent Total current assets Common stock: $0.001 par value; 1,000,000 shares authorized, 36,933 and 37,362 shares issued and outstanding as of March 31, 2023 and December 31, 2022, 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) Statistical Measurement [Domain] Cash payments included in the measurement of lease liabilities us-gaap_OperatingLeasePayments Maximum [Member] Minimum [Member] Current Statistical Measurement [Axis] Preferred stock: $0.001 par value; 20,000 shares authorized, no shares issued and outstanding as of March 31, 2023 and December 31, 2022 Preferred stock, shares issued (in shares) Property, Plant and Equipment Disclosure [Text Block] Geographical [Axis] Property, Plant and Equipment [Table Text Block] Geographical [Domain] Preferred stock, shares authorized (in shares) Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Preferred stock, par value (in dollars per share) Total foreign exchange losses, net Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value Hierarchy and NAV [Axis] Cash flow from operating activities: Statement [Line Items] us-gaap_NumberOfOperatingSegments Number of Operating Segments Accounts receivable, net of allowance of $912 and $736 as of March 31, 2023 and December 31, 2022, respectively Furniture and Fixtures [Member] us-gaap_NumberOfReportableSegments Number of Reportable Segments AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member] Additional paid-in capital Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] AOCI Attributable to Parent [Member] Stockholders’ equity: Short-term marketable securities Leasehold Improvements [Member] us-gaap_OtherNonoperatingExpense Other expenses Other income (expense), net Other Nonoperating Income (Expense) Long-Lived Tangible Asset [Axis] us-gaap_NonoperatingIncomeExpense Total other income (expense), net Long-Lived Tangible Asset [Domain] Segment Reporting Disclosure [Text Block] 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 Interest income us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Net increase in cash, cash equivalents and restricted cash us-gaap_Liabilities Total liabilities us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash used in financing activities Commitments and contingencies (Note 8) Executive Officer [Member] us-gaap_OperatingIncomeLoss Income from operations us-gaap_ContractWithCustomerLiabilityRevenueRecognized Contract with Customer, Liability, Revenue Recognized us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash provided by operating activities Other income (expense), net: Prepaid expenses and other current assets us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash provided by (used in) investing activities Cost of revenues us-gaap_GrossProfit Gross profit us-gaap_ContractWithCustomerLiability Contract with Customer, Liability us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation Payments for taxes related to net share settlement of equity awards us-gaap_PaymentsForRepurchaseOfCommonStock Repurchase of common stock Retained Earnings [Member] Proceeds from exercise of stock options Revenues Title of Individual [Domain] Proceeds from issuance of common stock through employee stock purchase plan Title of Individual [Axis] us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1 Stock Repurchase Program, Remaining Authorized Repurchase Amount Additional Paid-in Capital [Member] Common Stock [Member] Preferred Stock [Member] Authorized Dollar Value Equity Components [Axis] Equity Component [Domain] qlys_SharebasedCompensationArrangementBySharebasedPaymentAwardTargetPercentage Share-based Compensation Arrangement by Share-based Payment Award, Target Percentage The target percentage for vesting of equity-based award under share based payment arrangement. Remaining performance obligations, period (Year) Remaining performance obligations Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Foreign Exchange Contracts for GBP and Euro [Member] Information related to foreign exchange contracts for BPG and Euro. Foreign Exchange Contracts for INR [Member] Information related to foreign exchange contracts for INR. us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest Income before income taxes Performance Shares, Tranche Three [Member] Information related to tranche three of performance shares. Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification out of Accumulated Other Comprehensive Income [Axis] Executive Officer 2 [Member] Represents executive officer 2. Reclassification out of Accumulated Other Comprehensive Income [Domain] Executive Officer 1 [Member] Represents executive officer 1. Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Disaggregation of Revenue [Table Text Block] Revenue from Contract with Customer [Text Block] Computer Equipment [Member] Document Quarterly Report Entity Incorporation, State or Country Code us-gaap_UnrecognizedTaxBenefits Unrecognized Tax Benefits General and Administrative Expense [Member] us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Accounting Policies [Abstract] Document Transition Report Basis of Accounting, Policy [Policy Text Block] Entity Interactive Data Current Selling and Marketing Expense [Member] Security Exchange Name Title of 12(b) Security Cost of Sales [Member] Research and Development Expense [Member] Income Statement Location [Axis] Income Statement Location [Domain] Antidilutive securities (in shares) us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Diluted (in shares) Diluted weighted average shares (in shares) Non-US [Member] Statement [Table] Statement of Financial Position [Abstract] Diluted (in dollars per share) Basic weighted average shares (in shares) Basic (in shares) us-gaap_EffectiveIncomeTaxRateContinuingOperations Effective Income Tax Rate Reconciliation, Percent Basic (in dollars per share) Statement of Cash Flows [Abstract] Statement of Stockholders' Equity [Abstract] us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 Income tax benefit Other comprehensive income (loss), net of tax us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent Other comprehensive income (loss), net of tax Income Statement [Abstract] Contract with Customer, Sales Channel [Axis] Contract with Customer, Sales Channel [Domain] Sales Channel, Directly to Consumer [Member] Sales Channel, Through Intermediary [Member] Issuance of common stock upon vesting of restricted stock units Represents amount of restricted stock award vested during period. Investments Classified by Contractual Maturity Date [Table Text Block] Lessee, Operating Lease, Supplemental Cash Flow Disclosure [Table Text Block] Tabular disclosure of lessee's supplemental cash flow information associated with operating lease. Lessee, Weighted Average Remaining Lease Term and Weighted Average Discount Rate [Table Text Block] Tabular disclosure of lessee's weighted average remaining lease term and weighted average discount rate. Description Of Business Policy [Policy Text Block] Disclosure of accounting policy for description of business. Risk and Uncertainties, Policy [Policy Text Block] Disclosure of accounting policy for risk and uncertainties. Issuance of common stock upon vesting of restricted stock units (in shares) Number of shares issued during period for restricted stock vested. Foreign Government Agencies [Member] Information related to foreign government agencies. Fair Value, Assets Measured on Recurring Basis [Table Text Block] Cash flow from financing activities: Other Geographic Areas [Member] Represents information related to other geographic areas. Other noncurrent liabilities The 2012 Equity Incentive Plan [Member] Represents plan 2012. Expected to vest, number of shares (in shares) Represents vested and expected to vest outstanding number Change in unrealized gains (losses) during the period us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent Amount reclassified into income during the period us-gaap_StockholdersEquity Total stockholders’ equity Balance Balance Deferred revenues, noncurrent Other comprehensive income (loss), net of tax Class of Stock [Axis] us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization Property and equipment and finance lease Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax Unrealized loss, securities Unrealized gains, securities Net change in unrealized gains (losses) on cash flow hedges, net of tax Amortized Cost