Real Estate and Other Assets Held For Sale and Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets, held for sale [Abstract]
Land held for development	$ 995				$ 0				$ 995	$ 0
Net real estate assets	995				0				995	0
Prepaid expenses and other assets	43				0				43	0
Real estate and other assets, net, held for sale	1,038				0				1,038	0
Discontinued Operations [Abstract]
Rental and other revenues									0	20,812	41,176
Operating expenses:
Rental property and other expenses									0	8,283	14,456
Depreciation and amortization									0	5,753	11,970
Total operating expenses									0	14,036	26,426
Interest expense									0	0	283
Income from discontinued operations									0	6,776	14,467
Impairments of real estate assets									0	(2,194)	0
Net gains on disposition of discontinued operations									384	63,792	29,455
Total discontinued operations	$ 0	$ 0	$ 0	$ 384	$ 12,362	$ 39,460	$ 14,092	$ 2,460	$ 384	$ 68,374	$ 43,922
Raleigh, NC Land Disposition (7/2014) [Member]
Operating expenses:
Number of land parcels included in real estaet and other assets, net, held for sale	2								2