Long-term Debt - Senior Secured and Convertible Subordinated Notes (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended		12 Months Ended
	Sep. 30, 2016	Jul. 31, 2016	Mar. 31, 2016	Sep. 30, 2016	Mar. 31, 2015	Sep. 30, 2016	Aug. 31, 2016	Sep. 30, 2015	Dec. 31, 2013	Sep. 30, 2011
Long-term debt
Debt instrument, face amount	$ 768,800			$ 768,800		$ 768,800		$ 573,900
Loss on extinguishment of debt				$ 8,700	$ 24,800
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%	7.25%	7.25%
Debt instrument, face amount								$ 150,000	$ 150,000
Early repayment premium amount	$ 7,000
Redemption of senior notes	$ 99,000	$ 47,250	$ 3,750
Redemption price as a percentage of principal amount redeemed	103.625%	103.625%
Senior Secured Notes 7.625 Percent
Long-term debt
Interest rate on secured notes (as a percent)	7.625%			7.625%		7.625%		7.625%		7.625%
Debt instrument, face amount										$ 400,000
Loss on extinguishment of debt						$ 21,300
Early repayment premium amount						15,300
Early repayment of interest amount						2,500
Premiums and accelerated amortization of unamortized debt issue costs charged to interest expense						3,500
Convertible Senior Subordinated Notes 8.75 Percent Due 2016
Long-term debt
Interest rate on secured notes (as a percent)					8.75%
Redemption of senior notes						49,000
Premiums and accelerated amortization of unamortized debt issue costs charged to interest expense						$ 3,500
Convertible Senior Subordinated Notes 8.75 Percent Due 2016 | Chairman and CEO
Long-term debt
Convertible senior subordinated notes								$ 1,160