Investments in real estate Land undergoing predevelopment and future development (Details) - North America $ in Thousands	Sep. 30, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)
Real Estate Properties [Line Items]
Land available for development | $	$ 238,728	$ 206,939
Future Value-creation Projects [Member]
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development | ft²	5,678,707