Borrowings - Schedule of Debt Redemption (Details)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
5 3/4% Senior Notes Maturing June 2019
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	5.75%	5.75%
7 1/2% Senior Notes Maturing September 2021
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	7.50%	7.50%
8 3/4% Senior Notes Maturing March 2022
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	8.75%	8.75%
7 1/4% Senior Notes Maturing February 2023
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	7.25%	7.25%
Senior Notes | 5 3/4% Senior Notes Maturing June 2019
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	5.75%
Senior Notes | 5 3/4% Senior Notes Maturing June 2019 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	7.50%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	105.625%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	103.75%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	101.875%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021 | Debt Instrument, Redemption, Period Four
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	8.75%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	104.375%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	102.188%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022 | Debt Instrument, Redemption, Period Four
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	7.25%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	103.625%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	102.41%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023 | Debt Instrument, Redemption, Period Four
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	101.208%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023 | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 6 3/4% Senior Notes Maturing March 20255 [Domain]
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	6.75%
Senior Notes | 6 3/4% Senior Notes Maturing March 20255 [Domain] | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Notes | 6 3/4% Senior Notes Maturing March 20255 [Domain] | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	105.063%
Senior Notes | 6 3/4% Senior Notes Maturing March 20255 [Domain] | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	103.375%
Senior Notes | 6 3/4% Senior Notes Maturing March 20255 [Domain] | Debt Instrument, Redemption, Period Four
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	101.688%
Senior Notes | 6 3/4% Senior Notes Maturing March 20255 [Domain] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%