Investments in Unconsolidated Real Estate Joint Ventures (Management, Leasing and Marketing Fees) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Management, Leasing and Marketing Fees [Line Items]
Fees paid by unconsolidated joint ventures	$ 1,065	$ 532
Development Fee [Member]
Management, Leasing and Marketing Fees [Line Items]
Fees paid by unconsolidated joint ventures	71	0
Loan Guarantee Fee [Member]
Management, Leasing and Marketing Fees [Line Items]
Fees paid by unconsolidated joint ventures	40	0
Management and Leasing Fee [Member]
Management, Leasing and Marketing Fees [Line Items]
Fees paid by unconsolidated joint ventures	844	479
Marketing Fee [Member]
Management, Leasing and Marketing Fees [Line Items]
Fees paid by unconsolidated joint ventures	$ 110	$ 53