Segment Information Building Acquisitions and Dispositions (Details) - Jun. 30, 2015 $ in Thousands	USD ($) ft² a bldg		USD ($) ft² a bldg
Land, Buildings and Improvements [Member]
Dispositions [Abstract]
Proceeds from Sale of Property | $	$ 116,100		$ 158,332
Number of Real Estate Properties Sold | bldg	23		30
Sold Real Estate Property, Square Feet	1,406,000		2,028,000
Southern California [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Residential Real Estate | $	$ 36,700		$ 36,700
Acquisitions [Abstract]
Number of real estate properties acquired | bldg	1		1
Acquired Real Estate Property, Square Feet	410,000		410,000
Minnesota [Member] | Land, Buildings and Improvements [Member]
Dispositions [Abstract]
Proceeds from Sale of Property | $	$ 5,800		$ 5,800
Number of Real Estate Properties Sold | bldg	1		1
Sold Real Estate Property, Square Feet	87,000		87,000
Richmond Hampton Roads [Member] | Land and Land Improvements [Member]
Dispositions [Abstract]
Sold Land, Acres | a	3.1		3.1
Richmond Hampton Roads [Member] | Land, Buildings and Improvements [Member]
Dispositions [Abstract]
Proceeds from Sale of Property | $	$ 110,300	[1]	$ 110,300	[2]
Number of Real Estate Properties Sold | bldg	22		22
Sold Real Estate Property, Square Feet	1,319,000		1,319,000
Southeastern PA [Member] | Land, Buildings and Improvements [Member]
Dispositions [Abstract]
Proceeds from Sale of Property | $	$ 0		$ 8,720
Number of Real Estate Properties Sold | bldg	0		1
Sold Real Estate Property, Square Feet	0		83,000
Other Segments [Member] | Land, Buildings and Improvements [Member]
Dispositions [Abstract]
Proceeds from Sale of Property | $	$ 0		$ 33,512
Number of Real Estate Properties Sold | bldg	0		6
Sold Real Estate Property, Square Feet	0		539,000

[1] Includes proceeds from the sale of 3.1 acres of land.

[2] Includes proceeds from the sale of 3.1 acres of land.