Debt And Lines Of Credit , Table - Schedule of debt and lines of credit (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Debt	$ 1,287,571	$ 1,268,191
Debt weighted average to maturity, years	7 years 1 month	7 years 4 months
Weighted average interest rate	5.30%	5.30%
Collateralized term loans - CMBS [Member]
Debt Instrument [Line Items]
Debt	627,016	629,229
Debt weighted average to maturity, years	4 years 9 months	5 years
Weighted average interest rate	5.50%	5.50%
Collateralized term loans - FNMA [Member]
Debt Instrument [Line Items]
Debt	373,400	364,581
Debt weighted average to maturity, years	11 years 1 month	11 years 4 months
Weighted average interest rate	4.20%	3.60%
Aspen and Series B-3 Preferred OP Units [Member]
Debt Instrument [Line Items]
Debt	48,822	48,822
Debt weighted average to maturity, years	8 years 10 months	9 years 3 months
Weighted average interest rate	6.90%	6.90%
Secured borrowing [Member]
Debt Instrument [Line Items]
Debt	83,611	81,682
Debt weighted average to maturity, years	13 years 1 month	13 years 3 months
Weighted average interest rate	11.20%	11.20%
Mortgage notes, other [Member]
Debt Instrument [Line Items]
Debt	$ 154,722	$ 143,877
Debt weighted average to maturity, years	3 years 2 months	3 years 3 months
Weighted average interest rate	3.60%	3.80%