Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating real estate, consolidated variable interest entities	$ 1,639,496	$ 1,211,605
Construction-in-progress, consolidated variable interest entities	43,393	15,313
Accumulated depreciation and amortization, consolidated variable interest entities	247,410	209,239
Mortgages payable, consolidated variable interest entities	$ 460,372	$ 439,120
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
Common shares of beneficial interest, shares authorized	100,000,000	100,000,000
Common shares of beneficial interest, shares issued	73,090,877	71,995,897
Common shares of beneficial interest, shares outstanding	73,090,877	71,995,897
5.417% Series 1 Cumulative Convertible Preferred Shares
Preferred shares, percentage	5.417%	5.417%
Preferred Shares, liquidation preference per share	$ 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 Shares
Preferred shares, percentage	5.00%	5.00%
Preferred Shares, liquidation preference per share	$ 25,000
Preferred shares, shares issued	6,000	0
Preferred shares, shares outstanding	6,000	0