Debt (Details) (USD $)	0 Months Ended		3 Months Ended	6 Months Ended
	Apr. 09, 2013	Mar. 26, 2013	Jun. 30, 2013	Jun. 30, 2013
5 1/4% Senior Notes due 2023
Long Term Debt
Debt issued		$ 400,000,000
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	198,300,000	301,700,000
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			$ 600,000	$ 2,600,000