Subsequent Events (Details) (USD $)	1 Months Ended		12 Months Ended				1 Months Ended	12 Months Ended		0 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Series C Preferred Stock [Member]	Oct. 31, 2006 Series C Depositary Share [Member]	Dec. 31, 2011 Series C Depositary Share [Member]	Oct. 02, 2006 Series C Depositary Share [Member]	Feb. 23, 2012 Issuance of Equity [Member] Series D Depositary Share [Member]	Mar. 15, 2012 Issuance of Equity [Member] Series C Preferred Stock [Member]	Feb. 23, 2012 Issuance of Equity [Member] Series C Depositary Share [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued				3,680,000					3,680,000	11,500,000
Ratio of Depositary Share to Underlying Preferred Stock									0.01	0.0
Preferred Stock, Dividend Rate, Percentage						7.375%		7.375%		6.625%
Proceeds from Issuance of Preferred Stock							$ 92,000,000			$ 287,500,000
Stock Issuance Costs	9,060,000	10,393,000	(19,453,000)	(1,000)	(113,000)		3,098,000			9,600,000
Preferred Stock, Redemption Amount										$ 277,900,000
Preferred Stock, Redemption Price Per Share						$ 2,500.00		$ 25.00			$ 25.00
Preferred Stock, Fixed Annual Dividend Per Share, Depository Shares								$ 1.84375				$ 25.0768229