Commitments and Contingencies - Guarantees of Indebtedness (Details) - Joint Venture Mortgage and Indebtedness - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Guarantees of Joint Venture Indebtedness:
Loan guarantee	$ 215.5	$ 211.6
Loan guarantees recoverable	$ 10.8	$ 10.8

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=115931803&loc=d3e12069-110248

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant