Debt (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended				1 Months Ended		9 Months Ended		0 Months Ended				3 Months Ended	9 Months Ended	1 Months Ended		9 Months Ended				1 Months Ended		9 Months Ended
	Jan. 31, 2012 Term Loan maturing in 2016	Sep. 30, 2012 Term Loan maturing in 2016	Sep. 30, 2012 Term Loan maturing in 2016 Minimum	Sep. 30, 2012 Term Loan maturing in 2016 Maximum	Aug. 31, 2012 7 3/8% senior notes, due 2012	Jan. 31, 2012 7 3/8% senior notes, due 2012	Sep. 30, 2012 7 3/8% senior notes, due 2012	Dec. 31, 2011 7 3/8% senior notes, due 2012	Aug. 31, 2012 7 3/4% senior notes, due 2016	Aug. 16, 2012 7 3/4% senior notes, due 2016	Sep. 30, 2012 7 3/4% senior notes, due 2016	Dec. 31, 2011 7 3/4% senior notes, due 2016	Sep. 30, 2012 7 3/8% senior notes, due 2012 and 7 3/4% senior notes, due 2016	Sep. 30, 2012 7 3/8% senior notes, due 2012 and 7 3/4% senior notes, due 2016	Aug. 31, 2012 6 1/8% senior notes, due 2019	Sep. 30, 2012 6 1/8% senior notes, due 2019	Sep. 30, 2012 6 1/8% senior notes, due 2019 Debt redemption before August 15, 2015	Sep. 30, 2012 6 1/8% senior notes, due 2019 Debt redemption on or after August 15, 2016	Sep. 30, 2012 6 1/8% senior notes, due 2019 Debt redemption on or after August 15, 2017	Sep. 30, 2012 6 1/8% senior notes, due 2019 Debt redemption on or after August 15, 2018	Aug. 31, 2012 6 3/8% Senior Notes, due 2022	Sep. 30, 2012 6 3/8% Senior Notes, due 2022	Sep. 30, 2012 6 3/8% Senior Notes, due 2022 Debt redemption before August 15, 2015	Sep. 30, 2012 6 3/8% Senior Notes, due 2022 Debt redemption on or after August 15, 2017	Sep. 30, 2012 6 3/8% Senior Notes, due 2022 Debt redemption on or after August 15, 2018	Sep. 30, 2012 6 3/8% Senior Notes, due 2022 Debt redemption on or after August 15, 2019	Sep. 30, 2012 6 3/8% Senior Notes, due 2022 Debt redemption on or after August 15, 2020
Long Term Debt
Additional borrowings	$ 275.0														$ 400.0						$ 350.0
Quarterly principal payment as a percent of the original principal amount			1.25%	3.75%
Maximum redemption of debt instrument (as a percent)																	35.00%						35.00%
Unpaid principal balance payment		158.0
Note stated interest rate (as a percent)							7.375%	7.375%			7.75%	7.75%				6.125%						6.375%
Redemption price of debt instrument (as a percent)																	106.125%	103.063%	101.531%	100.00%			106.375%	103.188%	102.125%	101.063%	100.00%
Repayment of debt					62.2	279.7			89.5	410.5
Gross amount of debt extinguished							358.1
Expenses recorded for tender and call premiums, loss on early extinguishment of debt, unamortized debt issuance cost write-off, and tender expenses							$ 13.9						$ 26.3	$ 26.3