Indebtedness (Narrative) (Details) (USD $)	6 Months Ended			3 Months Ended		3 Months Ended	6 Months Ended			1 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Minimum [Member] Fixed Rate Secured Debt [Member]	Jun. 30, 2011 Minimum [Member] Fixed Rate Unsecured Debt [Member]	Jun. 30, 2011 Maximum [Member] Fixed Rate Secured Debt [Member]	Jun. 30, 2011 Maximum [Member] Fixed Rate Unsecured Debt [Member]	Jun. 30, 2011 Unsecured Line of Credit - DRLP [Member]	Jun. 30, 2011 Unsecured Line of Credit - Consolidated Subsidiary [Member]	Jun. 30, 2011 Fixed Rate Secured Debt [Member]	Mar. 31, 2011 Fixed Rate Unsecured Debt [Member]	Jun. 30, 2011 Fixed Rate Unsecured Debt [Member]
Estimated rate of fixed rate secured debt, minimum									4.10%
Estimated rate of fixed rate secured debt, maximum									5.80%
Secured loans acquired									9
Face value from acquisition									$ 124,400,000
Liabilities assumed	130,474,000	4,503,000							125,000,000
Assumed weighted average interest rate									5.78
Weighted average remaining term (years)									5.0
Estimated effective interest rate of loan			4.40%		5.81%					6.96%
Repayment of corporate unsecured debt	43,377,000	387,860,000								42,500,000
Estimated trading values of fixed rate unsecured debt, percentage				100.00		121.00
Debt instrument covenant compliance							we were in compliance with all covenants under this line of credit.				We were in compliance with all such covenants
Borrowing capacity of unsecured lines of credit							850,000,000	30,000,000
Spread over LIBOR							2.75%	0.85%
No borrowings on DRLP							0	18,329,000
Interest rate on borrowings								1.04%
Maturity date of unsecured line of credit							February 2013	July 2012
Additional borrowings under unsecured lines of credit							200,000,000
Maximum borrowing capacity of unsecured lines of credit							$ 1,050,000,000
Current market rate of unsecured lines of credit								2.19%