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Market Value and Amortized Cost of Marketable Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2015
Jul. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Market Value $ 56,890us-gaap_MarketableSecuritiesCurrent $ 39,659us-gaap_MarketableSecuritiesCurrent
Amortized Cost 56,553xcra_MarketableSecuritiesAmortizedCost 39,454xcra_MarketableSecuritiesAmortizedCost
Corporate    
Schedule of Available-for-sale Securities [Line Items]    
Market Value 10,787us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 21,070us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Amortized Cost 10,744xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 20,884xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Government    
Schedule of Available-for-sale Securities [Line Items]    
Market Value 27,905us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		 5,045us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Amortized Cost 27,625xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		 5,038xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Collateralized Mortgage Backed Securities    
Schedule of Available-for-sale Securities [Line Items]    
Market Value 2,454us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		 1,920us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
Amortized Cost 2,467xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		 1,923xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
Asset-backed Securities    
Schedule of Available-for-sale Securities [Line Items]    
Market Value 15,744us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember		 11,624us-gaap_MarketableSecuritiesCurrent
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
Amortized Cost $ 15,717xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember		 $ 11,609xcra_MarketableSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember