Accounting for the Impairment or Disposal of Long-Lived Assets (Tables)

12 Months Ended

Dec. 31, 2015

Accounting for the Impairment or Disposal of Long-Lived Assets [Abstract]

Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]

Information on the operating properties the Company sold during the years ended December 31, 2015 and 2014 is as follows:

2015 Sales

Reportable Segment	Number of Buildings	Acres of Developable Land (unaudited)	Leaseable Square Feet (unaudited)	Gross Proceeds (in thousands)
Minnesota	2	—	222,642	$	25,700
Orlando	1	—	713,585	35,500
Richmond/Hampton Roads	22	3	1,319,299	110,054
South Florida	1	—	99,740	14,700
Southeastern PA	46	20	2,724,489	316,583
Tampa	2	—	60,800	5,225
Other	7	—	569,618	37,371
Total	81	23	5,710,173	$	545,133

2014 Sales

Reportable Segment	Number of Buildings	Acres of Developable Land (unaudited)	Leaseable Square Feet (unaudited)	Gross Proceeds (in thousands)
Houston	5	—	553,510	$	29,721
Maryland	23	19	1,367,569	185,460
Minnesota	1	—	191,336	41,000
New Jersey	27	51	1,790,893	164,767
Orlando	4	—	588,678	116,750
Southeastern PA	3	—	113,833	12,225
Other	2	—	134,510	8,655
Total	65	70	4,740,329	$	558,578

A summary of the results of operations for the properties classified as discontinued operations through the respective disposition dates is as follows (in thousands):

	For the Year Ended December 31,
	2015		2014			2013
Revenues	$	—	$	4,728		$	113,586
Operating expenses	—		(2,258		)	(41,875		)
Interest and other income	—		37			213
Interest expense	—		(557		)	(15,903		)
Depreciation and amortization	—		—			(29,566		)
Income before gain on property dispositions	—		1,950			26,455
Gain on property dispositions	—		46,631			95,384
Net income	$	—	$	48,581		$	121,839

Asset Impairment Charges [Table Text Block]

The impairment losses are for operating properties or land parcels and were in the reportable segments and for the amounts as indicated below (in thousands):

	Year Ended December 31,
Reportable Segment	2015		2014		2013
Richmond/Hampton Roads	$	13,755	$	—	$	—
Southeastern PA	2,328		106
Tampa	—		—		248
United Kingdom	—		—		—
Other	2,161		11		872
Total	$	18,244	$	117	$	1,120