Subsidiary Guarantors - Senior Notes (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Senior Notes [Line Items]
Carrying value of senior notes	$ 550,000,000	$ 300,000,000
Event of default for senior notes - failure of other debt payment at maturity in excess of this amount	50,000,000
Our ownership percentage of subsidiary guarantors of senior notes	100.00%
Event of default for senior notes - not discharged, bonded or insured judgment in excess of this amount	50,000,000
Senior Notes Due 2020 [Member]
Senior Notes [Line Items]
Interest rate of senior notes	6.625%
Portion of proceeds from senior notes used to repay outstanding term debt	200,000,000
Senior notes are redeemable at a premium declining from this percentage	103.313%
Percentage of original aggregate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Interest rate of senior notes	4.75%
Portion of proceeds from senior notes used to repurchase shares of common stock	$ 200,000,000
Senior notes are redeemable at a premium declining from this percentage	103.563%
Percentage of original aggregate principle amount of senior notes included in repurchase price at change of control	101.00%