Background Schedule of rentable square feet (Details)	Sep. 30, 2014 sqft
Real Estate Properties [Line Items]
Area of Real Estate Property	18,458,379
Square Footage of Real Estate Property, Future Development	13,100,000
Total Rentable Square Footage of Asset Base	31,617,818
Operating properties [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property	16,373,416
Development [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property	1,941,186
Redevelopment [Member]
Real Estate Properties [Line Items]
Area of Real Estate Property	143,777
Near-term value-creation projects in North America (CIP)
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	1,926,331
Land held for future development in North America
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	10,983,108
Land subject to sale negotiations
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	250,000