Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Investments in Real Estate
Capitalized interest costs	$ 1.1	$ 0.3	$ 3.0	$ 1.5
Depreciation expense	$ 13.7	$ 10.7	$ 38.9	$ 29.7
Buildings | Minimum
Investments in Real Estate
Useful lives			27 years
Buildings | 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			15 years