Consolidating Financial Statements Text (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Oct. 01, 2007
Senior Exchangeable Notes due 2012 at a fixed interest rate of 3.75%
Debt Instrument [Line Items]
Issuance Date of Debt Instrument	October 2007
Debt Instrument, Face Amount	$ 0	$ 300,000,000	$ 300,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Debt Instrument Date of Maturity	2012
Debt Instrument, Maturity Date, Description	October 2012
Extinguishment of Debt, Amount	300,000,000
Senior Exchangeable Notes due 2015 at a fixed interest rate of 4.50%
Debt Instrument [Line Items]
Issuance Date of Debt Instrument	August 2009
Debt Instrument, Face Amount	172,500,000	172,500,000
Debt Instrument, Interest Rate, Stated Percentage	4.50%
Debt Instrument, Maturity Date, Description	August 2015
Senior Notes due 2022 at a fixed interest rate of 3.75% [Member]
Debt Instrument [Line Items]
Issuance Date of Debt Instrument	March 2012
Debt Instrument, Face Amount	325,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Debt Instrument, Maturity Date, Description	2022
Senior Notes due 2022 at a fixed interest rate of 3.75% [Member]
Debt Instrument [Line Items]
Issuance Date of Debt Instrument	March 2012
Debt Instrument, Face Amount	$ 325,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Debt Instrument, Maturity Date, Description	2022