Summary Of Significant Accounting Policies Consolidated Statement of Cash Flows - Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accounting Policies [Abstract]
Total interest costs incurred			$ 83,803	$ 83,485
Interest capitalized			(12,660)	(14,139)
Interest expense	$ 24,313	$ 21,733	71,143	69,346
Cash paid for interest, net of amounts capitalized (1)			66,921	91,319	[1]
Cash paid for income taxes			300	274
Mortgage loans assumed with acquisition			34,385	18,666
DownREIT operating partnership units redeemed for common shares			18,679	0
DownREIT operating partnership units issued with acquisition			0	7,742
Shares issued under dividend reinvestment plan			$ 1,523	1,468
Prepayment premium on senior note				$ 19,200

[1] (1) 2015 includes $19.2 million related to early extinguishment of debt.