Business (Narratives) (Details)	3 Months Ended
	Mar. 31, 2013 property sqft	Mar. 31, 2012 tenant
Additional disclosures
Square footage of all real estate properties	39,000,000
Number of real estate properties	422
Number of tenants		124
Occupancy rate	98.80%
Managed Reits
Additional disclosures
Square footage of all real estate properties	78,600,000
Number of real estate properties	703
Number of tenants	211
Occupancy rate	98.40%