Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Investments in Real Estate
Capitalized interest costs	$ 1.0	$ 1.0	$ 2.3	$ 2.2
Depreciation expense	$ 19.2	$ 15.9	$ 37.1	$ 31.0
Building | Minimum
Investments in Real Estate
Useful lives	27 years
Building | Maximum
Investments in Real Estate
Useful lives	40 years
Building Improvements | Minimum
Investments in Real Estate
Useful lives	1 year
Building Improvements | Maximum
Investments in Real Estate
Useful lives	10 years