Long-term Debt (Details 2) (USD $) In Millions, unless otherwise specified	1 Months Ended			3 Months Ended
	Mar. 31, 2011 7-5/8% Senior secured notes	Dec. 31, 2012 7-5/8% Senior secured notes	Sep. 30, 2012 7-5/8% Senior secured notes	Dec. 31, 2012 7-5/8% Senior secured notes Period commencing after March 31, 2015 Maximum	Dec. 31, 2012 7-5/8% Senior secured notes Period commencing after March 31, 2015 Minimum	Dec. 31, 2012 7-5/8% Senior secured notes On or prior to March 31, 2014	Dec. 31, 2012 7-5/8% Senior secured notes On or prior to March 31, 2014 Maximum	Dec. 31, 2012 7-5/8% Senior secured notes Any 12-month period ending on or prior to March 31, 2014	Dec. 31, 2012 7-5/8% Senior secured notes Any 12-month period ending on or prior to March 31, 2014 Maximum	Dec. 31, 2012 7-5/8% Senior secured notes On or prior to March 31, 2015	Mar. 31, 2011 11-3/8% senior secured notes
Long-term debt
Additional borrowings	$ 400.0
Net proceeds from senior secured notes	$ 392.8
Interest rate on secured notes (as a percent)	7.625%	7.625%	7.625%								11.375%
Debt instrument redemption price (as a percent)				103.80%	100.00%			103.00%
Percentage of the principal amount of the debt instrument which the entity may redeem with proceeds from qualified equity offerings							35.00%		10.00%
Redemption price of debt instrument if redeemed with proceeds from qualified equity offerings (as a percent)						107.60%
Debt instrument redemption price in addition to a make-whole premium (as a percent)										100.00%