Long-term Debt - Interest and Debt Maturities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Aug. 31, 2016	Mar. 31, 2016	Dec. 31, 2013	Sep. 30, 2011
Long-term debt
Interest expense	$ 43,300	$ 64,900	$ 46,900
Non-cash interest expense	3,973	$ 6,180	$ 2,175
Interest expense associated with debt transactions	$ 3,100
Weighted average interest rate (as a percent)	4.00%	5.20%
Future maturities of long-term debt
2017	$ 7,785
2018	7,785
2019	7,785
2020	7,785
2021	7,785
Thereafter	729,879
Total long-term debt	768,804
Term Loan Facility
Long-term debt
Required quarterly repayments due	1,900
Senior Secured Notes, 7.625 Percent and 7.25 Percent
Long-term debt
Interest expense	$ 7,000	$ 21,300
Senior Secured Notes 7.625 Percent
Long-term debt
Interest rate on secured notes (as a percent)	7.625%	7.625%					7.625%
7.25% Senior notes, due January 2019
Long-term debt
Interest rate on secured notes (as a percent)	7.25%	7.25%		7.25%	7.25%	7.25%