Equity and Capital Noncontrolling Interest of Limited Partners (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended			12 Months Ended
	Dec. 31, 2011	Feb. 24, 2012	Dec. 31, 2010	Dec. 31, 2011 Parent Company [Member]	Dec. 31, 2010 Parent Company [Member]
Limited Partners' Capital Account [Line Items]
Parent Company, Ownership Percentage of Outstanding Common Partnership Units of Operating Partnership				99.80%	99.80%
Noncontrolling Interest in Operating Partnerships	$ 13.1		$ 10.8
Series D preferred units, par value	$ 50,000,000		$ 50,000,000
Distributions Paid To Preferred Unit Holders	7.45%
General Partners' Capital Account, Units Outstanding		89,921,858	81,886,872
Partners' Capital Account, Units	90,099,022		82,064,036
Limited Partners' Capital Account, Units Outstanding	177,164		177,164