Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Parenthetical) (Details) (Unconsolidated Joint Ventures [Member], USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Unconsolidated Joint Ventures [Member]
Straight-line rent adjustments	$ 4.0	$ 5.6	$ 8.1	$ 13.8
"Above" and "below" market rent adjustments, net	$ 29.2	$ 30.4	$ 58.7	$ 67.2