Indebtedness (Unsecured Line of Credit) (Details) (USD $)		6 Months Ended
	Dec. 31, 2012 Line of Credit [Member]	Jun. 30, 2013 Unsecured Line of Credit DRLP [Member]
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.
Current Market Rate Of Unsecured Lines Of Credit		1.70%
Debt Instrument, Basis Spread on Variable Rate		1.25%
Line of Credit Facility, Interest Rate at Period End		1.45%
Borrowing capacity of unsecured line of credit		850,000,000
Maturity date		Dec. 01, 2015
Line of Credit Facility Increase		400,000,000
Line of credit balance	$ 285,000,000	$ 88,000,000