Property Dispositions (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) property	Sep. 30, 2014 USD ($) property	Sep. 30, 2015 USD ($) property	Sep. 30, 2014 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Document Fiscal Year Focus			2015
Proceeds from Sale of Real Estate	$ 67,345	$ 55,569	$ 93,727	$ 62,788
Gain (Loss) on Sale of Properties	$ 27,755	$ 27,558	$ 34,215	$ 29,598
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%
Parent Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Sale of Properties	$ 27,755	$ 27,558	$ 34,215	$ 29,598
Revenues	142,068	133,559	423,596	401,733
Operating expenses	89,467	85,923	268,262	262,574
Provision for impairment	$ 0	$ 0	$ 0	$ 225
Operating Segments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of operating properties sold | property	2	4	4	6
Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of operating properties sold | property	0	2	0	5