Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Operating real estate, consolidated variable interest entities	$ 2,188,736	$ 2,188,736	$ 1,703,202
Construction-in-progress, consolidated variable interest entities	28,277	28,277	44,896
Accumulated depreciation and amortization, consolidated variable interest entities	374,970	374,970	335,735
Mortgages payable, consolidated variable interest entities	$ 388,489	$ 388,489	$ 413,681
Preferred shares, authorized	15,000,000	15,000,000	15,000,000
Preferred shares, par value	$ 0.01	$ 0.01	$ 0.01
Common shares of beneficial interest, par value	$ 0.01	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized	100,000,000	100,000,000	100,000,000
Common shares of beneficial interest, shares issued	77,774,645	77,774,645	76,727,394
Common shares of beneficial interest, shares outstanding	77,774,645	77,774,645	76,727,394
5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 399,896 shares issued and outstanding
Preferred shares, percentage	5.417%	5.417%	5.417%
Preferred shares, liquidation preference	$ 25	$ 25	$ 25
Preferred shares, shares issued	399,896	399,896	399,896
Preferred shares, shares outstanding	399,896	399,896	399,896
5.0% Series C Cumulative Redeemable Preferred
Preferred shares, percentage		5.00%	5.00%
Preferred shares, liquidation preference	$ 25,000	$ 25,000	$ 25,000
Preferred shares, shares issued	6,000	6,000	6,000
Preferred shares, shares outstanding	6,000	6,000	6,000