Acquisitions and Dispositions (Summary of Significant Assumptions Utilized in Estimates) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 months
Minimum [Member]
Discount rate	7.19%
Exit capitalization rate	6.09%
Lease-up period (months)	9
Minimum [Member] | Industrial Buildings [Member]
Rental rate per square foot	2.75
Minimum [Member] | Medical Office Properties [Member]
Rental rate per square foot	16.10
Maximum [Member]
Discount rate	8.78%
Exit capitalization rate	7.40%
Lease-up period (months)	19
Maximum [Member] | Industrial Buildings [Member]
Rental rate per square foot	3.59
Maximum [Member] | Medical Office Properties [Member]
Rental rate per square foot	26.14