Components Of Rental Income (Schedule Of Principal Components Of Rental Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Cost reimbursement	$ 29,171		$ 25,714		$ 82,603		$ 80,083
Percentage rent	1,667		1,673		5,167		4,598
Other	3,217		2,227		7,801		6,191
Total rental income	147,515		134,014		429,972		401,452
Commercial Real Estate [Member]
Minimum rents	106,344		98,654		313,934		293,622
Residential Real Estate [Member]
Minimum rents	$ 7,116	[1]	$ 5,746	[1]	$ 20,467	[1]	$ 16,958	[1]

[1] Residential minimum rents consist of the rental amounts for residential units at Rollingwood Apartments, The Crest at Congressional Plaza Apartments, Santana Row and Bethesda Row.