Long-term Debt (Details 2) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended		6 Months Ended			1 Months Ended	6 Months Ended		6 Months Ended
	Mar. 31, 2014 7-5/8% Senior secured notes	Sep. 30, 2011 7-5/8% Senior secured notes	Sep. 30, 2013 7-5/8% Senior secured notes	Mar. 31, 2014 7-5/8% Senior secured notes Period commencing after March 31, 2015 Maximum	Mar. 31, 2014 7-5/8% Senior secured notes Period commencing after March 31, 2015 Minimum	Mar. 31, 2014 7-5/8% Senior secured notes On or prior to March 31, 2015	Dec. 31, 2013 71/4% Senior notes, due January 2019	Mar. 31, 2014 71/4% Senior notes, due January 2019	Sep. 30, 2013 71/4% Senior notes, due January 2019	Mar. 31, 2014 71/4% Senior notes, due January 2019 Period commencing after January 15, 2016 Maximum	Mar. 31, 2014 71/4% Senior notes, due January 2019 Period commencing after January 15, 2016 Minimum	Mar. 31, 2014 71/4% Senior notes, due January 2019 On or prior to January 15, 2016	Mar. 31, 2014 71/4% Senior notes, due January 2019 On or prior to January 15, 2016 Maximum
Long-term debt
Additional borrowings		$ 400.0					$ 150.0
Net proceeds from senior secured notes		$ 392.8					$ 146.2
Interest rate on secured notes (as a percent)	7.625%	7.625%	7.625%				7.25%	7.25%	7.25%
Debt instrument redemption price (as a percent)				103.80%	100.00%					103.625%	100.00%
Percentage of the principal amount of the debt instrument which the entity may redeem with proceeds from qualified equity offerings													35.00%
Redemption price of debt instrument if redeemed with proceeds from qualified equity offerings (as a percent)												107.25%
Debt instrument redemption price in addition to a make-whole premium (as a percent)						100.00%						100.00%
Purchase price of debt instrument, if there is a change in control (as a percent)	101.00%							101.00%