Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Operating real estate, consolidated variable interest entities	$ 1,751,718	$ 1,676,866
Construction-in-progress, consolidated variable interest entities	83,902	102,583
Accumulated depreciation and amortization, consolidated variable interest entities	306,861	296,165
Mortgages payable, consolidated variable interest entities	$ 476,944	$ 469,184
Preferred shares, authorized	15,000,000	15,000,000
Preferred shares, par value	$ 0.01	$ 0.01
Common shares of beneficial interest, par value	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized	100,000,000	100,000,000
Common shares of beneficial interest, shares issued	75,622,504	75,540,804
Common shares of beneficial interest, shares outstanding	75,622,504	75,540,804
5.417% Series 1 Cumulative Convertible Preferred
Preferred shares, percentage	5.417%	5.417%
Preferred shares, liquidation preference	$ 25	$ 25
Preferred shares, shares issued	399,896	399,896
Preferred shares, shares outstanding	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
Preferred shares, shares issued	6,000	6,000
Preferred shares, shares outstanding	6,000	6,000