Equity and Capital - Preferred Stock and Preferred Units (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended		3 Months Ended
	Feb. 16, 2012	Feb. 09, 2012	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Parent Company [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.625%
Preferred Stock, Liquidation Preference Per Share	$ 25		$ 25		$ 25
Proceeds from Issuance of Preferred Stock and Preference Stock			$ 241,450,000	$ 0
Other Preferred Stock Dividends and Adjustments			7,000,000
Parent Company [Member] | Preferred Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	10
Partnership Interest [Member]
Class of Stock [Line Items]
Preferred Stock, Liquidation Preference Per Share			$ 25		$ 25
Proceeds from Issuance of Preferred Stock and Preference Stock	241,500,000		241,450,000	0
Preferred Stock, Discount To Par		3.75%
Preferred Unit Dividends And Other Adjustments		$ 1,000,000	$ 13,308,000	$ 5,850,000