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Investments in real estate Development and redevelopment projects (Details)
Dec. 31, 2014
sqft
Real Estate Properties [Line Items]  
Area of Real Estate Property 18,729,282us-gaap_AreaOfRealEstateProperty
Development  
Real Estate Properties [Line Items]  
Number of real estate properties 7us-gaap_NumberOfRealEstateProperties
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= are_DevelopmentMember
Redevelopment  
Real Estate Properties [Line Items]  
Number of real estate properties 2us-gaap_NumberOfRealEstateProperties
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= are_RedevelopmentMember
North America | Development  
Real Estate Properties [Line Items]  
Area of Real Estate Property 1,727,758us-gaap_AreaOfRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= are_DevelopmentMember
/ us-gaap_StatementGeographicalAxis
= us-gaap_NorthAmericaMember
North America | Redevelopment  
Real Estate Properties [Line Items]  
Area of Real Estate Property 143,777us-gaap_AreaOfRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= are_RedevelopmentMember
/ us-gaap_StatementGeographicalAxis
= us-gaap_NorthAmericaMember