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Stock-Based Compensation - Option and RSA Activity Rollforward (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Shares Available for Grant    
Shares available for grant beginning balance (in shares) 11,612us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant  
Options granted (in shares) (283)anet_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodsharesavailableforgrant  
Early exercised shares repurchased (in shares) 10anet_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesAvailableforGrantEarlyExercisedSharesRepurchased  
Shares available for grant ending balance (in shares) 11,560us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant 11,612us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Number of Shares Underlying Outstanding Options and RSAs (in thousands)    
Beginning balance, options (in shares) 13,654us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber  
Options granted (in shares) 283us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross  
Options exercised (in shares) (773)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised  
Options canceled (in shares) (221)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod  
Early exercised shares repurchased (in shares) 0anet_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsEarlyExercisedSharesRepurchased  
Ending balance, options (in shares) 12,943us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 13,654us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Vested and exercisable (in shares) 3,371us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber  
Vested and expected to vest (in shares) 11,454us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber  
Weighted- Average Exercise Price per Share    
Outstanding beginning balance (usd per share) $ 17.63us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice  
Options granted (usd per share) $ 66.05us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice  
Options exercised (usd per share) $ 6.92us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice  
Options canceled (usd per share) $ 20.66us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice  
Early exercised shares repurchased $ 3.95anet_SharebasedCompensationArrangementsbySharebasedPaymentAwardEarlyExercisedSharesRepurchasedWeightedAverageExercisePrice  
Outstanding ending balance (usd per share) $ 19.27us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 17.63us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Vested and exercisable (usd per share) $ 6.29us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice  
Vested and expected to vest (usd per share) $ 17.80us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice  
Weighted- Average Remaining Contractual Term and Aggregate Intrinsic Value of Stock Options Outstanding    
Weighted-average remaining contractual term of stock options outstanding 8 years 1 month 6 days 8 years 3 months 18 days
Weighted-average remaining contractual term of stock options vested and exercisable 7 years 2 months 12 days  
Weighted-average remaining contractual term of stock options vested and expected to vest 8 years 11 days  
Aggregate intrinsic value of stock options outstanding $ 661,984us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue $ 598,775us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
Aggregate intrinsic value of stock options outstanding vested and exercisable 216,548us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1  
Aggregate intrinsic value of stock options outstanding vested and expected to vest $ 605,313us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue