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Balance Sheet Accounts (Schedule of Available-for-sale Securities) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 21,268us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 33,145us-gaap_AvailableForSaleSecuritiesAmortizedCost
Fair Value 21,272us-gaap_AvailableForSaleSecurities 33,259us-gaap_AvailableForSaleSecurities
Unrealized Holding Gains 4extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments 114extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
Unrealized Holding Losses 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
Cash equivalents    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 951us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
567us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
Fair Value 951us-gaap_AvailableForSaleSecurities
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
567us-gaap_AvailableForSaleSecurities
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
Unrealized Holding Gains 0extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
0extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
Unrealized Holding Losses 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_CashEquivalentsMember
Short-term investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 20,317us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
32,578us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
Fair Value 20,321us-gaap_AvailableForSaleSecurities
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
32,692us-gaap_AvailableForSaleSecurities
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
Unrealized Holding Gains 4extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
114extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
Unrealized Holding Losses 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ extr_ScheduleOfAvailableForSaleSecuritiesByMajorCategoryOfInvestmentAxis
= us-gaap_ShortTermInvestmentsMember
Money market funds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 951us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
567us-gaap_AvailableForSaleSecuritiesAmortizedCost
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= us-gaap_MoneyMarketFundsMember
Fair Value 951us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
567us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
Unrealized Holding Gains 0extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
0extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
Unrealized Holding Losses 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MoneyMarketFundsMember
U.S. corporate debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 20,317us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
32,578us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Fair Value 20,321us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
32,692us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Unrealized Holding Gains 4extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
114extr_AvailableforsaleSecuritiesGrossUnrealizedGainAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
Unrealized Holding Losses $ 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember
$ 0extr_AvailableforsaleSecuritiesGrossUnrealizedLossAccumulatedInvestments
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DomesticCorporateDebtSecuritiesMember