Accounting for the Impairment or Disposal of Long-Lived Assets Asset Impairment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Property, Plant and Equipment [Line Items]
Impairment - real estate assets	$ 0	$ 1,036,000	$ 0	$ 16,775,000
Carolinas Richmond [Member]
Property, Plant and Equipment [Line Items]
Impairment - real estate assets				13,400,000
Southeastern PA [Member]
Property, Plant and Equipment [Line Items]
Impairment - real estate assets				2,300,000
DC Metro [Member]
Property, Plant and Equipment [Line Items]
Impairment - real estate assets		$ 1,000,000		$ 1,000,000