Long-term Debt - Discounted Carrying Values (Details) - USD ($)	Jun. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Dec. 31, 2013
Long-term debt
Debt instrument, face amount	$ 567,000,000	$ 573,900,000
Carrying amount of long-term debt, net of discounts and debt issue costs	557,048,000	562,330,000
Less current portion	(4,250,000)	(4,250,000)
Long-term debt	552,798,000	558,080,000
Senior secured term loan, due March 2022
Long-term debt
Debt instrument, face amount	420,750,000	423,938,000	$ 425,000,000
Carrying amount of long-term debt, net of discounts and debt issue costs	412,426,000	414,490,000
7.25% Senior notes, due January 2019
Long-term debt
Debt instrument, face amount	146,250,000	150,000,000		$ 150,000,000
Carrying amount of long-term debt, net of discounts and debt issue costs	$ 144,622,000	$ 147,840,000
Interest rate on long-term debt (as a percent)	7.25%	7.25%	7.25%	7.25%