Investments in real estate, net Development and redevelopment projects (Details)	Sep. 30, 2015 ft² property
Real Estate Properties [Line Items]
Area of Real Estate Property | ft²	19,943,739
Development [Member]
Real Estate Properties [Line Items]
Number of real estate properties	10
Redevelopment [Member]
Real Estate Properties [Line Items]
Number of real estate properties	2
North America [Member] | Development [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property | ft²	3,300,000
North America [Member] | Redevelopment [Member]
Real Estate Properties [Line Items]
Number of real estate properties	3
Area of Real Estate Property | ft²	525,482
Operating properties [Member] | North America [Member] | Development [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property | ft²	713,524
Unconsolidated Joint Venture | Development [Member]
Real Estate Properties [Line Items]
Number of real estate properties	2