<DefinitionAndReference>
  <Element Id="us-gaap_Assets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsVestedAndExpectedToVestOutstandingNumber">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Other Than Options Vested And Expected To Vest Outstanding Number.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AllocatedShareBasedCompensationExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ComprehensiveIncomeNoteTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ReconciliationOfBasicAndDilutedIncomePerShareTextBlock">
    <definition>Reconciliation of basic and diluted income per share.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringCharges">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrices">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Exercise Prices.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FurnitureAndFixturesGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAuthorized">
    <definition>Share based compensation arrangement by share based payment award increase in number of shares authorized.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SalesPurchasesOfDeferredCompensationPlanSecuritiesNet">
    <definition>Sales (purchases) of deferred compensation plan securities, net.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ConstructionInProgressGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsReceivableGrossCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryRawMaterials">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_StockBasedCompensationExpenseIncludedInConsolidatedStatementsOfIncomeTextBlock">
    <definition>Stock Based Compensation Expense Included In Consolidated Statements Of Income.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_NetStockBasedCompensationExpense">
    <definition>Net stock-based compensation expense.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCompensationPlanFixedIncomeSecurities">
    <definition>Deferred Compensation Plan Fixed Income Securities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LeaseholdImprovementsGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedIncomeTaxesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsAtCarryingValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsNetNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_EquipmentAndSoftware">
    <definition>Equipment and software.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityPublicFloat">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_PeriodOfSettlementForReceivableBalancesDays">
    <definition>Period of settlement for receivable balances, days.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentPeriodEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquireIntangibleAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageExpectedDividend">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsReceivableNetCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCompensationPlanEquitySecurities">
    <definition>Deferred Compensation Plan Equity Securities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefits">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueDisclosuresTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCurrentReportingStatus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_PercentageOfWorkforceReduction">
    <definition>Percentage of workforce reduction.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_GainOnSubstantiveTerminationOfRetireeMedicalPlan">
    <definition>Gain on substantive termination of retiree medical plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCostsOfSalesRecognizedUponShipmentsToDistributors">
    <definition>Deferred costs of sales recognized upon shipments to distributors.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Land">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsPayableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityFilerCategory">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringReserve">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetIncomeLoss">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableIntrinsicValues">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Intrinsic Values.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ScheduleOfInventoryTextBlock">
    <definition>Schedule of Inventory Text Block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredIncomeOnShipmentsToDistributors">
    <definition>Deferred income on shipments to distributors.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedIncomeTaxesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxExaminationLiabilityRefundAdjustmentFromSettlementWithTaxingAuthority">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DecreaseIncreaseInAdvancesToDistributors">
    <definition>Decrease (increase) in advances to distributors.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsAndContingencies2009">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_CostsOfSalesRecognizedUponSellThroughToEndCustomers">
    <definition>Costs of sales recognized upon sell-through to end customers.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerms">
    <definition>Share Based Compensation Arrangement By ShareBased Payment Award Options Outstanding Weighted Average Remaining Contractual Terms.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GrossProfit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_IncreaseDecreaseInNonQualifiedDeferredCompensationPlan">
    <definition>(Payments for) Proceeds from deferred compensation plan securities, net.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockValueOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SellingGeneralAndAdministrativeExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SummaryOfStockOptionActivityTextBlock">
    <definition>Summary of stock option activity.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccountsReceivable">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerms">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Terms.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentType">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentFiscalYearFocus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredCompensationLiabilityCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_BusinessExitCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInOperatingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_AdvancesToDistributors">
    <definition>Advances to distributors.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SalesRevenueNetPercentageOfNetSales">
    <definition>Sales revenue net percentage of net sales.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_IncreaseDecreaseInOtherDeferredRevenue">
    <definition>Increase (decrease) in other deferred revenue.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfLineOfCreditFacilitiesTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SalesToOemsAsPercentageOfNetSales">
    <definition>Sales to OEMs as a Percentage of Net Sales.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueAndCreditsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesAndStockholdersEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockParOrStatedValuePerShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestInPeriodAggregateIntrinsicValue">
    <definition>Share Based Compensation Arrangement By ShareBased Payment Award EquityInstruments Other Than Options Vested And Expected To Vest In Period Aggregate Intrinsic Value.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueAssetsMeasuredOnRecurringBasisCashAndCashEquivalents">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherDeferredCreditsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_CurrentFiscalYearEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsOfDividendsCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_MaximumPercentageOfAverageAggregatePriceConcessionsOnListPrice">
    <definition>Maximum percentage of average aggregate price concessions on list price.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCompensationPlanMutualFunds">
    <definition>Deferred Compensation Plan Mutual funds.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SalesToDistributorsAsPercentageOfNetSales">
    <definition>Sales To Distributors as a Percentage of Net Sales.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ComponentsOfComprehensiveIncomeTextBlock">
    <definition>Components of Comprehensive Income.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueRefundPayments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SeveranceCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_PerSharePriceOfCommonStockUnderEmployeeStockPurchasePlan">
    <definition>Per Share Price Of Common Stock Under Employee Stock Purchase Plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SummaryOfActivityForRestrictedStockUnitsAndPerformanceBasedRestrictedStockUnitsTextBlock">
    <definition>Summary of activity for Restricted Stock Units and Performance based Restricted Stock Units Text Block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryFinishedGoods">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationUnrecognizedCompensationCostsOnNonvestedAwardsWeightedAveragePeriodOfRecognition">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestInPeriodWeightedAverageGrantDateFairValue">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested And Expected To Vest In Period Weighted Average Grant Date Fair Value.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueRevenueRecognized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedLiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockholdersEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementPercentageOfPurchasePriceLowerThanFairMarketValueOfCommonStock">
    <definition>Share Based Compensation Arrangement Percentage Of Purchase Price Lower Than Fair Market Value Of Common Stock.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareDiluted">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_AmendmentFlag">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InvestmentIncomeInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Liabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_NumberOfParticipantsInDeferredCompensationPlan">
    <definition>Number of participants in deferred compensation plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ReductionOfPositionsNet">
    <definition>Reduction of positions, net.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesAuthorized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_MinimumPercentageOfAverageAggregatePriceConcessionsOnListPrice">
    <definition>Minimum percentage of average aggregate price concessions on list price.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_IncreaseInSharesReservedUnderEsppForFutureIssuance">
    <definition>Increase in shares reserved under ESPP for future issuance.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromStockPlans">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfSubsequentEventsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCompensationPlanRestrictedCashEquivalents">
    <definition>Deferred compensation plan - restricted cash equivalents.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SalesRevenueNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValue">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Aggregate Intrinsic Value.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdvancesOnInventoryPurchases">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateContinuingOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingAggregateIntrinsicValues">
    <definition>ShareBased Payment Award Options Outstanding Aggregate Intrinsic Values.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentFiscalPeriodFocus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ComprehensiveIncomeNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryWorkInProcess">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityRegistrantName">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_AllowanceForSalesReturns">
    <definition>Allowance for sales returns.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxesPaid">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCostOfSalesOnShipmentsToDistributors">
    <definition>Deferred cost of sales on shipments to distributors.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DepreciationAndAmortization">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_NetSalesByCustomerTypeAndNetSalesToSignificantCustomersTextBlock">
    <definition>Net Sales By Customer Type And Net Sales To Significant Customers Text Block.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_BuildingsAndImprovementsGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_MaximumTimePeriodToSubmitClaimForReceivingPriceConcession">
    <definition>Maximum time period  to submit the claim for receiving price concession.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdditionalPaidInCapitalCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_NonQualifiedDeferredCompensationPlanTextBlock">
    <definition>Non-Qualified Deferred Compensation Plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_NumberOfShareholderDerivativeLawsuitsFiled">
    <definition>Number of shareholder derivative lawsuits filed.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueByArrangementDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredRevenueAdditions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriodWeightedAverageGrantDateFairValuePeriod">
    <definition>ShareBasedCompensationArrangementByShareBased Payment Award Equity Instruments Other Than Options Forfeited In Period Weighted Average GrantDate Fair Value Period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_PercentageOfFacilityFee">
    <definition>Percentage of facility fee.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SharesWithheldForEmployeeTaxes">
    <definition>Shares withheld for employee taxes.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermLineOfCredit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedTerm">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LossContingencyPendingClaimsNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementInputsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_LossGainOnDeferredCompensationPlanSecurities">
    <definition>Loss (gain) on deferred compensation plan securities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_AssumptionsUsedToEstimateFairValueOfStockOptionsRsusAndPrsusTextBlock">
    <definition>Assumptions Used To Estimate Fair Value Of Stock Options Rsus And Prsus.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ResearchAndDevelopmentExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeServiceShareBasedCompensationUnrecognizedCompensationCostsOnNonvestedAwards">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInDeferredRevenue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrices">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Prices.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DividendsPayableAmountPerShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LossContingencyNewClaimsFiledNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredIncomeAndAllowancesOnSalesToDistributorsTextBlock">
    <definition>Deferred Income and Allowances on Sales to Distributors.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInOtherOperatingAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CostOfGoodsAndServicesSold">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCentralIndexKey">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockDividendsPerShareDeclared">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Other Than Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInInvestingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_AccountsReceivableFromDistributorsAsPercentageOfTotalAccountsReceivables">
    <definition>Accounts Receivable From Distributors As A Percentage Of Total Accounts Receivables.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SubsequentEventsTextBlock">
    <definition>Subsequent Events.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredCompensationPlanAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerms">
    <definition>Share Based Compensation Arrangement By ShareBased Payment Award Options Exercisable Weighted Average Remaining Contractual Terms.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SignificantCommitmentRemainingMinimumAmountCommitted">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInInventories">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_SharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan">
    <definition>Shares available for future issuance under the ESPP.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeRelatedLiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityWellKnownSeasonedIssuer">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueAssetsMeasuredOnRecurringBasisDerivativeFinancialInstrumentsAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredCompensationArrangementWithIndividualMaximumContractualTerm">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityVoluntaryFilers">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RetainedEarningsAccumulatedDeficit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerm">
    <definition>Share Based Compensation Arrangement By Share Based Payment Award Other Than Options Outstanding Weighted Average Remaining Contractual Term.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsNetCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriod">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredIncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_DeferredCompensationPlanMarketableSecurities">
    <definition>Deferred compensation plan - marketable securities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCommonStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_EarnedDistributorPriceConcessions">
    <definition>Earned distributor price concessions</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="altr_CompensationExpenseBenefitDeferredCompensationPlan">
    <definition>Compensation expense (benefit) - deferred compensation plan.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TaxBenefitFromStockOptionsExercised">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
</DefinitionAndReference>
