Investments in Real Estate (Acquisitions) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) property	Sep. 30, 2016 property
Business Acquisition [Line Items]
Number of real estate properties | property	205	187
Purchase price	$ 415.8
Land parcels
Business Acquisition [Line Items]
Number of real estate properties | property			4
Purchase price	55.3	$ 47.6
Data Centers
Business Acquisition [Line Items]
Purchase price	346.2
Technology Manufacturing
Business Acquisition [Line Items]
Purchase price	$ 14.3