Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investments in Real Estate
Capitalized interest costs	$ 0.6	$ 1.2	$ 2.9	$ 3.4
Depreciation expense	$ 19.6	$ 16.8	$ 56.7	$ 47.7
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