Long-term Debt (Details 2) (7-5/8% Senior secured notes, USD $) In Millions, unless otherwise specified	1 Months Ended			6 Months Ended
	Mar. 31, 2011	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2013 Period commencing after March 31, 2015 Maximum	Mar. 31, 2013 Period commencing after March 31, 2015 Minimum	Mar. 31, 2013 On or prior to March 31, 2014	Mar. 31, 2013 On or prior to March 31, 2014 Maximum	Mar. 31, 2013 Any 12-month period ending on or prior to March 31, 2014	Mar. 31, 2013 Any 12-month period ending on or prior to March 31, 2014 Maximum	Mar. 31, 2013 On or prior to March 31, 2015
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%
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%