Subsequent Events (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 19, 2013 Repurchase Of Equity [Member] Series F Preferred Stock [Member]	Feb. 19, 2013 Subsequent Event [Member] Series H Preferred Stock [Member]	Feb. 19, 2013 Subsequent Event [Member] Series F Preferred Shares And Series H Preferred Shares [Member]	Jan. 25, 2013 Subsequent Event [Member] Issuance Of Equity [Member] Series L Preferred Stock [Member]
Subsequent Events [Line Items]
Preferred Stock, Par or Stated Value Per Share							$ 25.00
Sale of Stock, Number of Shares Issued in Transaction							12,000,000
Proceeds from the issuance of preferred shares	$ 290,971	$ 238,842	$ 0				$ 290,853
Stock Redeemed Or Called During Period Value	$ 72,248		$ 35,600			$ 262,500
Preferred Stock Dividend Rate Percentage				6.75%	6.75%		5.40%
Preferred Stock Redemption Price Per Share							$ 25.00