Background Schedule of rentable square feet (Details)	Sep. 30, 2015 ft²
Real Estate Properties [Line Items]
Area of Real Estate Property	19,943,739
Square Footage of Real Estate Property, Future Development	11,527,268
Total Square Footage of Asset Base	31,471,007
Operating properties [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property	16,803,766
Development [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property	2,614,491
Redevelopment [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property	525,482
Near-term value-creation projects in North America (CIP)
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	1,310,186
Land held for future development in North America
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	10,217,082
North America [Member] | Land held for future development in North America
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	3,797,375
Asia [Member] | Land held for future development in North America
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	6,419,707