Real Estate and Other Assets Held For Sale and Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Assets, held for sale [Abstract]
Land	$ 11,488		$ 11,488		$ 0
Buildings and tenant improvements	81,936		81,936		0
Land held for development	2,597		2,597		0
Less accumulated depreciation	(34,281)		(34,281)		0
Net real estate assets	61,740		61,740		0
Accrued straight line rents receivable	3,873		3,873		0
Deferred leasing costs, net	1,825		1,825		0
Prepaid expenses and other assets	721		721		0
Real estate and other assets, net, held for sale	68,159		68,159		0
Discontinued operations [Abstract]
Rental and other revenues	0	6,262	0	13,260
Operating expenses:
Rental property and other expenses	0	2,416	0	4,866
Depreciation and amortization	0	1,851	0	4,055
Total operating expenses	0	4,267	0	8,921
Income from discontinued operations	0	1,995	0	4,339
Impairment of real estate assets	0	(1,066)	0	(2,194)
Net gains on disposition of discontinued operations	0	13,163	384	14,407
Total discontinued operations	$ 0	$ 14,092	$ 384	$ 16,552
Richmond, VA Office Properties Disposition (6/2014) [Member]
Operating expenses:
Number of office properties included in real estate and other assets, net, held for sale	11		11
Raleigh, NC Office Properties Disposition (6/2014) [Member]
Operating expenses:
Number of office properties included in real estate and other assets, net, held for sale	5		5