Related Parties (Narrative) (Details) (USD $)	1 Months Ended		3 Months Ended		6 Months Ended					1 Months Ended	12 Months Ended	6 Months Ended
	Nov. 30, 2012 jvs	Feb. 29, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 property	Jun. 30, 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	Jun. 30, 2013 Tenancy In Common [Member] jvs	Aug. 06, 2012 Tenancy In Common [Member]
Related Party Transaction [Line Items]
Net accounts receivable, related parties			$ 1,500,000		$ 1,500,000		$ 1,800,000
Accounts payable and accrued expenses, related parties			6,000,000		6,000,000		6,300,000
Management fees revenue, related parties			1,400,000	1,600,000	2,800,000	3,300,000
Ownership percentage in joint ventures		47.80%					75.00%	20.00%	50.00%			10.00%	79.60%
Number of real estate joint ventures	3											2
Number of operating properties sold					10					9	54
Proceeds from sale of unconsolidated real estate joint venture, gross	20,900,000	29,100,000										8,900,000
Gain on sale of real estate joint venture and partnership interests	$ 8,600,000	$ 3,500,000	$ 83,000	$ 0	$ 11,592,000	$ 5,562,000