Redeemable Noncontrolling Interests / Redeemable Partnership Units (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Fair value of Series G convertible preferred units and Series D-13 cumulative redeemable preferred units	$ 50,561	$ 50,561

The fair value of shares that would be issued, determined under the conditions specified in the contract if the settlement were to occur at the reporting date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6940734&loc=d3e22047-110879

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