Summary Of Significant Accounting Policies Consolidated Statement of Cash Flows - Supplemental Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounting Policies [Abstract]
Total interest costs incurred	$ 32,276	$ 29,209
Interest capitalized	(6,092)	(5,451)
Interest expense	26,184	23,758
Cash paid for interest, net of amounts capitalized	31,832	25,089
Cash paid for income taxes	57	197
DownREIT operating partnership units issued with acquisition of noncontrolling interest	0	5,918
DownREIT operating partnership units redeemed for common shares	0	951
Shares issued under dividend reinvestment plan	$ 477	$ 541