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Summary of Significant Accounting Policies (Narrative) (Details) - New Accounting Pronouncement, Early Adoption, Effect - Accounting Standards Update 2017-05 - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
New Accounting Pronouncement, Early Adoption [Line Items]
Gain on sale of ground lease business	$ 178.9	$ 178.9
Expected Incremental Gain to be Recorded Retrospectively
New Accounting Pronouncement, Early Adoption [Line Items]
Gain on sale of ground lease business	$ 55.5	$ 55.5

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- Definition

Gain (loss) from sale or disposal of an organization or integrated set of activities (for example, but not limited to, a partnership or corporation) engaged in providing a product or service in a commercial, industrial, or professional environment.

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- Definition

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+ References

No definition available.

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