Consolidated Balance Sheets (Parenthetical) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Rental properties, accumulated depreciation	$ 954,806,000	$ 883,174,000
Common Shares, par value	$ 0.01	$ 0.01
Common Shares, shares authorized	100,000,000	100,000,000
Common Stock, Shares, Issued	80,677,733	77,226,443
Preferred Shares, par value	$ 0.01	$ 0.01
Preferred Shares, shares authorized	25,000,000	25,000,000
Treasury Shares, common shares	3,121,730	2,878,587
Series C Preferred Shares [Member]
Preferred Shares, shares issued	5,394,050	5,394,050
Preferred Shares, liquidation preference	$ 134,851,250	$ 134,851,250
Series E Preferred Shares [Member]
Preferred Shares, shares issued	3,447,381	3,447,381
Preferred Shares, liquidation preference	$ 86,184,525	$ 86,184,525
Series G Preferred Stock [Member]
Preferred Shares, shares issued	6,000,000	6,000,000
Preferred Shares, liquidation preference	$ 150,000,000	$ 150,000,000