Summary Of Significant Accounting Policies Consolidated Statement of Cash Flows - Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounting Policies [Abstract]
Total interest costs incurred	$ 34,159	$ 32,580
Interest capitalized	(5,714)	(4,547)
Interest expense	28,445	28,033
Cash paid for interest, net of amounts capitalized	29,405	32,485
Cash paid for income taxes	4	7
DownREIT operating partnership units issued with acquisition	18,920	0
Mortgage loans assumed with acquisition	8,903	0
DownREIT operating partnership units redeemed for common shares	0	7,551
Shares issued under dividend reinvestment plan	$ 429	$ 455