Long-term Debt (Details 3) (USD $) In Millions, unless otherwise specified	6 Months Ended		1 Months Ended			6 Months Ended	12 Months Ended		6 Months Ended				6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	May 31, 2012 8 7/8% Senior Secured Second Lien Notes due January 15, 2017	Jun. 30, 2013 8 7/8% Senior Secured Second Lien Notes due January 15, 2017	Dec. 31, 2012 8 7/8% Senior Secured Second Lien Notes due January 15, 2017	Jun. 30, 2013 8 7/8% Senior Secured Second Lien Notes due January 15, 2017 RTS	Dec. 31, 2012 8 7/8% Senior Secured Second Lien Notes due January 15, 2017 RTS	May 10, 2012 8 7/8% Senior Secured Second Lien Notes due January 15, 2017 RTS	Jun. 30, 2013 8 7/8% Senior Secured Second Lien Notes due January 15, 2017 RTS Maximum	Jun. 30, 2013 Revolving credit facility due through October 2016	Dec. 31, 2012 Revolving credit facility due through October 2016 RTS	May 10, 2012 Revolving credit facility due through October 2016 RTS	Jun. 30, 2013 Eurodollar loans under the revolving credit facility RTS item	Jun. 30, 2013 Base rate loans under the revolving credit facility Federal funds rate RTS	Jun. 30, 2013 Base rate loans under the revolving credit facility Eurodollar rate RTS
Long-term debt
Issuance of long-term debt			$ 350.0
Fixed interest rate (as a percent)				8.875%	8.875%			8.875%
Percentage of principal amount at which the entity may redeem some or all of notes prior to May 15, 2014						100.00%
Percentage of aggregate principal amount at which the entity may redeem notes with the net cash proceeds of certain equity offerings prior to May 15, 2014									35.00%
Transaction fees and expenses, including legal, accounting and other fees and expenses							14.4
Initial purchasers' discount	0	1.7					1.7
Maximum borrowing capacity												140.0
Maximum possible increase in aggregate amount of revolving loans											$ 10
Number of business days prior to interest period for determination of LIBOR rate													2
Value from which to subtract base rate to determine denominator in interest rate calculation													1
Basis to determine variable interest rate										LIBOR				federal funds rate	1 Month Eurodollar Rate
Margin added to the reference rate (as a percent)														0.50%	1.00%