Commitments And Contingencies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) partnership property	Dec. 31, 2014 USD ($) partnership property	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Long-term Purchase Commitment [Line Items]
Operating leases, rental expense	$ 3,200,000	$ 5,300,000		$ 5,600,000
Number of real estate properties | property	2	2
Capital leases, total assets	$ 16,800,000	$ 16,800,000
Capital leases, accumulated depreciation	13,800,000	13,000,000
Capital leases, future minimum payments	34,561,000
Capital leases, future minimum payments, interest	13,600,000
Capital leases, future minimum payments, present value of net minimum payments	21,000,000
Shares issued in exchange of interests		0	$ 0
Increase in equity for operating partnership units	111,000	0	$ 0
Total assets	$ 3,901,945,000	$ 3,805,915,000
Minimum [Member]
Long-term Purchase Commitment [Line Items]
Operating leases, term range, in years	1 year
Maximum [Member]
Long-term Purchase Commitment [Line Items]
Operating leases, term range, in years	25 years
Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 63,900,000
Capital Additions [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, period (in months)	12 months
Capital Additions [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, period (in months)	36 months
Development Addition [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 24,000,000
Future investment amount	$ 30,100,000
DownREIT [Member]
Long-term Purchase Commitment [Line Items]
Number of real estate joint ventures | partnership	2	3
Shares issued in exchange of interests	$ 100,000	$ 0
Aggregate redemption value	$ 51,000,000	$ 52,000,000