CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Tenant and other receivables, allowance for doubtful accounts	$ 8,107,000	$ 7,248,000
Intangible assets, accumulated amortization	$ 13,795,000	$ 13,117,000
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	70,353,000	69,983,000
Common stock, shares outstanding	70,353,000	69,983,000
Series B Preferred Stock [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	$ 0.01
Preferred shares, authorized	25,000,000	25,000,000
Preferred Stock, Shares Issued	6,900,000	6,900,000
Preferred shares, outstanding	6,900,000	6,900,000
Liquidation preference	$ 172,500,000	$ 172,500,000
Series D Preferred Stock [Member]
Preferred shares, par value	$ 0.01	$ 0.01
Preferred shares, authorized	25,000,000	25,000,000
Preferred Stock, Shares Issued	5,000,000	5,000,000
Preferred shares, outstanding	5,000,000	5,000,000
Liquidation preference	$ 120,000,000	$ 120,000,000