Indebtedness (Unsecured Lines of Credit) (Details) (USD $)	9 Months Ended			1 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jul. 31, 2012	Jul. 31, 2012 Unsecured Line of Credit - Consolidated Subsidiary [Member]	Sep. 30, 2012 Line of Credit [Member]
Borrowing capacity of unsecured lines of credit				$ 30,000,000	$ 850,000,000
Maturity date					Dec. 31, 2015
Line of credit balance					0
Line of Credit Facility, Increase, Additional Borrowings					400,000,000
Line of Credit Facility, Maximum Borrowing Capacity					1,250,000,000
Line of Credit Facility, Covenant Compliance	we were in compliance with all covenants under this line of credit.
Debt Instrument, Basis Spread on Variable Rate			0.85%		1.25%
Borrowings (payments) on lines of credit, net	$ (20,293,000)	$ 111,247,000		$ 20,300,000