Debt 3.25% Convertible Senior Debentures (Details) (USD $)	3 Months Ended		12 Months Ended
	Jun. 30, 2012	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Losses on Extinguishment of Debt			$ 35,092,000	$ 0	$ 25,552,000
Write Off Of Deferred Debt Issuance Cost			12,466,000	6,012,000	6,636,000
Long-term Debt, Gross			2,473,927,000	2,381,929,000
3.25% Convertible Senior Debentures, Due 2035 [Member]
Debt Instrument, Face Amount			977,500,000
Amortization of Financing Costs			800,000	1,000,000	2,000,000
Debt Instrument, Interest Rate, Stated Percentage			3.25%
Deferred Finance Costs, Gross			17,600,000
Total consideration to complete debt extinguishment	25,000,000				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
Losses on Extinguishment of Debt	1,800,000				25,600,000
Payments of Debt Extinguishment Costs					1,300,000
Write Off Of Deferred Debt Issuance Cost		4,600,000
Extinguishment of Debt, Amount					525,000,000
Long-term Debt, Gross			$ 427,500,000	$ 452,500,000