Indebtedness (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Debt Instrument [Line Items]
Repayments of mortgage loans	$ 19,288	$ 25,558
Proceeds from Issuance of Secured Debt	11,186	0
Secured Debt	282,716		290,819
Issuance of Debt [Member]
Debt Instrument [Line Items]
Interest rate on debt	4.84%
Proceeds from Issuance of Secured Debt	45,000
Secured Debt	11,200
Repayment of Debt [Member]
Debt Instrument [Line Items]
Repayments of mortgage loans	$ 17,900
Interest rate on debt	7.70%