Property Dispositions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Real Estate	$ 55,569	$ 48,999	$ 62,788	$ 131,363
Gain (Loss) on Sale of Properties	27,558	16,108	29,598	29,235
Wholly Owned Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percent interest sold	100.00%	100.00%	100.00%	100.00%
Segment, Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues		3,120		13,970
Operating expenses		1,580		7,107
Parent Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Sale of Properties	27,558	56	29,598	1,773
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	0	16,052	0	27,462
Revenues	133,559	120,318	401,733	363,002
Operating expenses	85,923	78,777	262,574	238,617
Operating income from discontinued operations	0	1,540	0	6,863
Provision for impairment	$ 0	$ 6,000	$ 225	$ 6,000
Operating Segments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of operating properties sold	4	4	6	8
Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of operating properties sold	2	0	5	0