Investments in Unconsolidated Companies (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			6 Months Ended	12 Months Ended
	Dec. 31, 2011 entities	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2010 Dugan Realty [Member]	Dec. 31, 2009 Dugan Realty [Member]
Schedule of Equity Method Investments [Line Items]
Rental revenue	$ 272,937	$ 228,378	$ 254,787	$ 42,500	$ 85,700
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 10,709	$ 19,202	$ 9,760	$ 6,400	$ 12,500
Number of unconsolidated joint ventures in which equity interests held	20