Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Operating real estate, consolidated variable interest entities	$ 1,709,234	$ 1,709,234	$ 1,676,866
Construction-in-progress, consolidated variable interest entities	81,463	81,463	102,583
Accumulated depreciation and amortization, consolidated variable interest entities	314,866	314,866	296,165
Mortgages payable, consolidated variable interest entities	$ 474,775	$ 474,775	$ 469,184
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	75,641,074	75,641,074	75,540,804
Common shares of beneficial interest, shares outstanding	75,641,074	75,641,074	75,540,804
5.417% Series 1 Cumulative Convertible Preferred
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