Summary Of Significant Accounting Policies Consolidated Statement of Cash Flows - Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Total interest costs incurred			$ 92,520	$ 83,803
Interest capitalized			(18,568)	(12,660)
Interest expense	$ 26,287	$ 24,313	73,952	71,143
Cash paid for interest, net of amounts capitalized			70,486	66,921
Cash paid for income taxes			342	300
Mortgage loans refinanced			166,823	0
Mortgage loans assumed with acquisition			79,401	34,385
DownREIT operating partnership units issued with acquisition of noncontrolling interest			5,918	0
DownREIT operating partnership units redeemed for common shares			2,569	18,679
Shares issued under dividend reinvestment plan			$ 1,528	$ 1,523