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		6 Months Ended
	Feb. 16, 2012	Feb. 09, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 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		$ 25
Proceeds from Issuance of Preferred Stock and Preference Stock					$ 241,386,000	$ 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		$ 25
Proceeds from Issuance of Preferred Stock and Preference Stock	241,400,000				241,386,000	0
Preferred Stock, Discount To Par		3.75%
Preferred Unit Dividends And Other Adjustments		$ 1,000,000	$ 5,396,000	$ 5,850,000	$ 18,704,000	$ 11,700,000