Equity and Capital - Preferred Stock and Preferred Units (Details) (USD $)	0 Months Ended		3 Months Ended		9 Months Ended			0 Months Ended			3 Months Ended		9 Months Ended
	Aug. 23, 2012 Parent Company [Member]	Feb. 16, 2012 Parent Company [Member]	Sep. 30, 2012 Parent Company [Member]	Jun. 30, 2012 Parent Company [Member]	Sep. 30, 2012 Parent Company [Member]	Sep. 30, 2011 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Aug. 23, 2012 Parent Company [Member] Preferred Stock [Member]	Feb. 16, 2012 Parent Company [Member] Preferred Stock [Member]	Feb. 09, 2012 Partnership Interest [Member]	Sep. 30, 2012 Partnership Interest [Member]	Sep. 30, 2011 Partnership Interest [Member]	Sep. 30, 2012 Partnership Interest [Member]	Sep. 30, 2011 Partnership Interest [Member]	Dec. 31, 2011 Partnership Interest [Member]
Class of Stock [Line Items]
Common Stock, Shares, Issued								3,000,000	10,000,000
Preferred Stock, Dividend Rate, Percentage	6.00%	6.625%
Preferred Stock, Liquidation Preference Per Share	$ 25	$ 25	$ 25		$ 25		$ 25				$ 25		$ 25		$ 25
Proceeds from Issuance of Preferred Stock and Preference Stock					$ 313,505,000	$ 0		$ 72,100,000	$ 241,400,000				$ 313,505,000	$ 0
Other Preferred Stock Dividends and Adjustments			2,300,000	7,000,000
Preferred Stock, Discount To Par										3.75%
Preferred Unit Dividends And Other Adjustments										$ 1,000,000	$ 7,932,000	$ 5,850,000	$ 26,636,000	$ 17,550,000