Debt (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended		9 Months Ended
	Apr. 09, 2013	Mar. 26, 2013	Sep. 30, 2013
5 1/4% Senior Notes due 2023
Long Term Debt
Debt issued		$ 400.0
Effective interest rate ( as a percent)		5.25%
5 1/4% Senior Notes due 2023 | Debt redemption period April 15, 2018 to April 14, 2019
Long Term Debt
Redemption price of debt instrument (as a percent)			102.625%
5 1/4% Senior Notes due 2023 | Debt redemption period April 15, 2019 to April 14, 2020
Long Term Debt
Redemption price of debt instrument (as a percent)			101.75%
5 1/4% Senior Notes due 2023 | Debt redemption period April 15, 2020 to April 14, 2021
Long Term Debt
Redemption price of debt instrument (as a percent)			100.875%
5 1/4% Senior Notes due 2023 | Debt redemption before April 15, 2016
Long Term Debt
Redemption price of debt instrument (as a percent)			105.25%
Maximum redemption of debt instrument (as a percent)			35.00%
5 1/4% Senior Notes due 2023 | Debt redemption on or after April 15, 2021
Long Term Debt
Redemption price of debt instrument (as a percent)			100.00%
6 3/4% senior notes, due 2015
Long Term Debt
Effective interest rate ( as a percent)		6.75%
Redemption price of debt instrument (as a percent)	100.00%
Redemption of debt	198.3	301.7
Expenses recorded related to tender offer and early payoff of Senior Notes related to tender premiums, unamortized debt issuance cost write-off, and tender expenses			$ 2.6