Noncash Investing and Financing Activities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Jun. 30, 2011
Other Significant Noncash Transactions [Line Items]
Accrued dividends and distributions payable	$ 43,547	$ 43,547	$ 41,717
Additions to real estate assets accrued but not yet paid		23,107	31,721
Noncash or Part Noncash Acquisition, Debt Assumed	177,296
Outlet Shoppes at Gettysburg [Member]
Other Significant Noncash Transactions [Line Items]
Debt Conversion, Converted Instrument, Amount	4,522
Noncash or Part Noncash Acquisition, Debt Assumed	$ (40,631)