Consolidated Statement of Equity (Parenthetical) - $ / shares	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Shares pursuant to dividend reinvestment plan	65,171,000	68,206,000	96,268	14,525,000	12,627,000	83,978
Shares due to exercise of employee stock options and issuance of directors' deferred stock	743,000	6,038,000	910	984,000	3,109,000	11,745
Issuance of partnership units pursuant to dividend reinvestment plan (in shares)	13,841,000			13,108,000
Limited Partner
Shares pursuant to dividend reinvestment plan		13,978,000	19,493			15,101
Twinbrook Metro Station
Number of partnership units issued in transaction (in shares)		469,740,000	1,416,071
Ashbrook Marketplace
Number of partnership units issued in transaction (in shares)		93,674,000
Dividend Distributions Payable
Distributions payable common stock, per share (in usd per share)	$ 0.55	$ 0.55	$ 0.53	$ 0.53	$ 0.53	$ 0.53
Distributions partnership units, per unit (in usd per share)	0.55	0.55	0.53	0.53	0.53	0.53
Series D Cumulative Redeemable Preferred Stock | Dividend Distributions Payable
Distributions payable on preferred stock, per share (in usd per share)	38.28	38.28	38.28	38.28	38.28	38.28
Series E Cumulative Redeemable Preferred Stock | Dividend Distributions Payable
Distributions payable on preferred stock, per share (in usd per share)	$ 37.50	$ 37.50	$ 37.50	$ 37.50	$ 37.50	$ 37.50