Summary Of Significant Accounting Policies Consolidated Statement of Cash Flows - Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accounting Policies [Abstract]
Total interest costs incurred	$ 27,559	$ 28,889
Interest capitalized	(3,830)	(4,721)
Interest expense	23,729	24,168
Cash paid for interest, net of amounts capitalized	20,635	22,837
Cash paid for income taxes	141	116
Mortgage loans assumed in acquisition	34,385	18,666
DownREIT operating partnership units issued with acquisition	0	7,742
DownREIT operating partnership units redeemed for common shares	4,281	4,114
Shares issued under dividend reinvestment plan	$ 537	$ 494