Preferred Stock and Stockholders' Equity (Details) (USD $)	1 Months Ended	5 Months Ended	12 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended
	Aug. 31, 2011	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Nov. 29, 2007 Series A Perpetual Stock [Member]	Dec. 31, 2011 Series A Perpetual Stock [Member]	Dec. 31, 2011 Series A Perpetual Stock [Member]	Dec. 31, 2010 Series A Perpetual Stock [Member]	Nov. 29, 2007 Series B Convertible Preferred Stock [Member]	Dec. 31, 2011 Series B Convertible Preferred Stock [Member]	Dec. 31, 2010 Series B Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Convertible Stock Initial Stated Value										$ 1,000
Preferred Stock Dividend Rate per Annum, Increase due to Passed Dividends Accrued and Unpaid								2.00%
Preferred Stock, Maximum Dividend Rate per Annum								16.00%
Preferred Stock, Redemption Amount									$ 199,000,000
Preferred Stock Redemption Premium							7,600,000
Dividends, Preferred Stock, Cash				25,927,000	19,531,000		1,400,000
Preferred Stock, Shares Issued						190,000				35,000
Payments for Repurchase of Preferred Stock and Preference Stock			0	190,000,000	0	190,000,000				35,000,000
Payments of Stock Issuance Costs						3,000,000				800,000
Preferred Stock Accretion Rate per Annum										6.00%
Aggregate Accretion of Series B Convertible Stock											9,600,000	7,100,000
Preferred Stock, Accretion Value for Conversion											1,000
Convertible Preferred Stock, Shares Issued per Aggregate Accretion Value Unit											14.44878
Stock Repurchase Program, Authorized Amount	45,000,000
Stock Repurchased During Period, Shares		534,101					190,000
Payments for Repurchase of Common Stock		$ 21,200,000	$ 21,170,000	$ 0	$ 0
Common Stock Repurchased Average Cost Per Share			$ 39.64