The fair value as of the reporting date of noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. The noncontrolling interest holder's ownership (or holders' ownership) may be in the form of common shares (regardless of class), limited partnership units (regardless of class), non-preferential membership interests, or any other form of common equity regardless of investee entity legal form.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph (12)(c)
-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph (16)(c)
-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph 14
-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-Subparagraph 15
-URI http://asc.fasb.org/extlink&oid=27011957&loc=SL6540498-122764

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

Commitments And Contingencies (Narrative) (Details)	3 Months Ended		12 Months Ended
Commitments And Contingencies (Narrative) (Details)	Mar. 31, 2016 USD ($) partnership	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) partnership
DownREIT [Member]
Long-term Purchase Commitment [Line Items]
Number of real estate joint ventures \| partnership	2		2
Shares issued in exchange of interests	$ 0	$ 100,000
Aggregate redemption value	55,000,000		$ 51,000,000
Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 62,000,000
Capital Additions [Member] \| Minimum [Member]
Long-term Purchase Commitment [Line Items]
Construction contract, period (in months)	12 months
Capital Additions [Member] \| Maximum [Member]
Long-term Purchase Commitment [Line Items]
Construction contract, period (in months)	36 months
Development Addition [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 24,000,000
Future investment amount	$ 30,400,000