Summary of Significant Accounting Policies - Real Estate (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments in Real Estate
Capitalized interest costs	$ 3.6	$ 1.1	$ 6.2	$ 2.2
Depreciation expense	$ 32.8	$ 30.8	$ 65.0	$ 59.9
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