Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Series G Preferred Units	Dec. 31, 2012 Series G Preferred Units	Mar. 31, 2013 Series H Preferred Units	Dec. 31, 2012 Series H Preferred Units	Mar. 31, 2013 Series C Preferred Stock	Dec. 31, 2012 Series C Preferred Stock	Mar. 31, 2013 Series I Preferred Stock	Dec. 31, 2012 Series I Preferred Stock
Tenant and other receivables, allowance (in dollars)	$ 20,947	$ 21,652
Deferred rents receivable, allowance (in dollars)	28,475	29,580
Debt and preferred equity investments, discount (in dollars)	11,251	13,572
Debt and preferred equity investments, allowance (in dollars)	$ 7,000	$ 7,000
Preferred Units, liquidation preference (in dollars per share)			$ 25.00	$ 25.00	$ 25.00	$ 25.00
Preferred Units, shares issued			1,902,000	1,902,000	80,000	80,000
Preferred Units, shares outstanding			1,902,000	1,902,000	80,000	80,000
Preferred stock, par value (in dollars per share)							$ 0.01	$ 0.01	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)							$ 25.00	$ 25.00	$ 25.00	$ 25.00
Preferred stock, shares issued							7,700,000	7,700,000	9,200,000	9,200,000
Preferred stock, shares outstanding							7,700,000	7,700,000	9,200,000	9,200,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	95,201,000	94,896,000
Common stock, shares outstanding	95,201,000	94,896,000
Treasury stock, shares	3,646,000	3,646,000