Summary Of Significant Accounting Policies Consolidated Statement of Cash Flows - Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounting Policies [Abstract]
Total interest costs incurred	$ 38,626	$ 34,159
Interest capitalized	(6,541)	(5,714)
Interest expense	32,085	28,445
Cash paid for interest, net of amounts capitalized	29,973	29,405
Cash paid for income taxes	0	4
DownREIT operating partnership units issued with acquisition	0	18,920
Mortgage loans assumed with acquisition	0	8,903
DownREIT operating partnership units redeemed for common shares	519	0
Shares issued under dividend reinvestment plan	$ 430	$ 429