Summary of Significant Accounting Policies - Real Estate (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Investments in Real Estate
Capitalized interest costs	$ 1.6	$ 0.6	$ 3.5	$ 2.9
Depreciation expense	$ 22.3	$ 19.6	$ 63.9	$ 56.7
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