Related Parties (Narrative) (Details) (USD $)	1 Months Ended		3 Months Ended					1 Months Ended	12 Months Ended
	Nov. 30, 2012 jvs	Feb. 29, 2012	Mar. 31, 2013 property	Mar. 31, 2012	Dec. 31, 2012	Nov. 30, 2012 Minimum [Member]	Nov. 30, 2012 Maximum [Member]	Nov. 30, 2012 Industrial Properties [Member] property	Dec. 31, 2012 Industrial Properties [Member] property
Related Party Transaction [Line Items]
Net accounts receivable, related parties			$ 1,400,000		$ 1,800,000
Accounts payable and accrued expenses, related parties			5,900,000		6,300,000
Management fees revenue, related parties			1,400,000	1,700,000
Ownership percentage in joint ventures		47.80%			75.00%	20.00%	50.00%
Number of real estate joint ventures	3
Number of operating properties sold			1					9	54
Proceeds from sale of unconsolidated real estate joint venture, gross	20,900,000	29,100,000
Gain on sale of real estate joint venture and partnership interests	$ 8,600,000	$ 3,500,000	$ 11,509,000	$ 5,562,000