Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Series C Preferred Shares [Member]	Dec. 31, 2011 Series C Preferred Shares [Member]	Dec. 31, 2012 Series D Preferred Stock [Member]	Dec. 31, 2011 Series D Preferred Stock [Member]	Dec. 31, 2012 Series E Preferred Shares [Member]	Dec. 31, 2011 Series E Preferred Shares [Member]	Dec. 31, 2012 Series F Preferred Stock [Member]	Dec. 31, 2011 Series F Preferred Stock [Member]
Real Estate Investment Property, Accumulated Depreciation	$ 375,684,000	$ 335,116,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	75,000,000	75,000,000
Common Stock, Shares, Issued	48,454,181	48,062,593
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	25,000,000	25,000,000
Preferred Stock, Shares Issued			5,400,000	5,400,000	0	4,600,000	3,450,000	3,450,000	5,000,000	0
Auction Market Preferred Securities, Stock Series, Liquidation Value			$ 135,000,000	$ 135,000,000	$ 0	$ 115,000,000	$ 86,250,000	$ 86,250,000	$ 125,000,000	$ 0
Treasury Stock, Shares	1,566,780	1,335,879