Consolidated Balance Sheets (Parenthetical) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Rental properties, accumulated depreciation	$ 711,384,000	$ 635,535,000
Common Shares, par value	$ 0.01	$ 0.01
Common Shares, shares authorized	100,000,000	100,000,000
Common Shares, shares issued	76,397,669	66,263,487
Preferred Shares, par value	$ 0.01	$ 0.01
Preferred Shares, shares authorized	25,000,000	25,000,000
Treasury Shares, common shares	2,732,736	2,616,406
Series C Preferred Shares [Member]
Preferred Shares, shares issued	5,399,050	5,399,050
Preferred Shares, liquidation preference	$ 134,976,250	$ 134,976,250
Series E Preferred Shares [Member]
Preferred Shares, shares issued	3,449,165	3,450,000
Preferred Shares, liquidation preference	$ 86,246,625	$ 86,250,000
Series F Preferred Stock [Member]
Preferred Shares, shares issued	5,000,000	5,000,000
Preferred Shares, liquidation preference	$ 125,000,000	$ 125,000,000