XML 13 R53.htm IDEA: XBRL DOCUMENT v2.4.1.9
Stock-Based Compensation (Valuation Assumptions) (Details) (Restricted Stock Units (RSUs) [Member], USD $)
3 Months Ended
Mar. 27, 2015
Rate
Mar. 28, 2014
Rate
Restricted Stock Units (RSUs) [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 0.70%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
0.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Dividend yield 2.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
1.90%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Weighted-average estimated fair value $ 32.20altr_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueAssumptionsWeightedAverageEstimatedFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
$ 30.40altr_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueAssumptionsWeightedAverageEstimatedFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember