Debt 3.25% Convertible Senior Debentures (Details) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Gains (Losses) on Extinguishment of Debt		$ 0	$ (25,552,000)	$ 0
Write Off Of Deferred Debt Issuance Cost		6,012,000	6,636,000	0
Long-term Debt, Gross	2,561,461,000	2,381,929,000	2,561,461,000
3.25% Convertible Senior Debentures, Due 2035 [Member]
Amortization of Financing Costs		1,000,000	2,000,000	2,000,000
Debt Instrument, Face Amount		977,500,000
Debt Instrument, Interest Rate, Stated Percentage		3.25%
Total consideration to complete debt extinguishment		498,800,000
Percent threshold average share price after stated period to allow cash distribution		120.00%
Percent stock price closes above conversion price for option of conversion		130.00%
Debt Instrument, Convertible, Conversion Price		$ 79.73
Gains (Losses) on Extinguishment of Debt			25,600,000
Payments of Debt Extinguishment Costs			1,300,000
Deferred Finance Costs, Gross		17,600,000
Write Off Of Deferred Debt Issuance Cost	4,600,000		4,600,000
Extinguishment of Debt, Amount			525,000,000
Long-term Debt, Gross	$ 452,500,000	$ 452,500,000	$ 452,500,000