Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 property	Dec. 31, 2011 property	Dec. 31, 2010 property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Real Estate									$ 73,576	$ 66,009	$ 34,918
Number of Real Estate Properties Sold									5	7	3
Revenues included in Discontinued Operations	122,002	119,432	129,243	126,243	123,596	122,419	124,038	123,045
Discontinued Operation, Tax Effect of Discontinued Operation									600	(289)	(166)
Wholly Owned Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest									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 included in Discontinued Operations									3,423	15,030	19,374
Operating Expenses									1,750	9,368	11,553
Other Operating Income (Expense), Net									0	3,458	6,729
Discontinued Operation, Tax Effect of Discontinued Operation									$ (18)	$ 106	$ (233)