CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Tenant and other receivables, allowance for doubtful accounts	$ 6,599,000	$ 6,236,000
Intangible assets, accumulated amortization	$ 10,643,000	$ 11,064,000
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	69,888,000	69,553,000
Common stock, shares outstanding	69,888,000	69,553,000
Series A Preferred Shares [Member]
Preferred shares, par value	$ 0.01	$ 0.01
Preferred shares, authorized	25,000,000	25,000,000
Preferred Stock, Shares Issued	4,600,000	4,600,000
Preferred shares, outstanding	4,600,000	4,600,000
Liquidation preference	$ 115,000,000	$ 115,000,000
Series B Preferred Shares [Member]
Preferred shares, par value	$ 0.01	$ 0.01
Preferred shares, authorized	25,000,000	25,000,000
Preferred Stock, Shares Issued	3,450,000	3,450,000
Preferred shares, outstanding	3,450,000	3,450,000
Liquidation preference	$ 86,250,000	$ 86,250,000
Series C Preferred Stock [Member]
Preferred shares, par value	$ 0.01
Preferred shares, authorized	25,000,000
Preferred Stock, Shares Issued	6,900,000
Preferred shares, outstanding	6,900,000
Liquidation preference	$ 172,500,000
Series D Preferred Stock [Member]
Preferred shares, par value	$ 0.01
Preferred shares, authorized	25,000,000
Preferred Stock, Shares Issued	4,800,000
Preferred shares, outstanding	4,800,000
Liquidation preference	$ 120,000,000