Borrowings - Schedule of Debt Redemption (Details)	12 Months Ended
	Sep. 30, 2018	Mar. 31, 2017
5 3/4% Senior Notes Maturing June 2019
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	5.75%
8 3/4% Senior Notes Maturing March 2022
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	8.75%
7 1/4% Senior Notes Maturing February 2023
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	7.25%
6 3/4% Senior Notes Maturing March of 2025
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	6.75%
5 7/8% Senior Notes Maturing October 2027
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	5.88%
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 | 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 (percent)	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 (percent)	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 (percent)	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 (percent)	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 Two
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	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 (percent)	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 (percent)	101.208%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023 | Debt Instrument, Redemption, Period Five
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	100.00%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	6.75%	6.75%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	100.00%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	105.063%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	103.375%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025 | Debt Instrument, Redemption, Period Four
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	101.688%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025 | Debt Instrument, Redemption, Period Five
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	100.00%
Senior Notes | 5 7/8% Senior Notes Maturing October 2027
Debt Instrument, Redemption [Line Items]
Debt instrument stated interest rate (percent)	5.875%
Senior Notes | 5 7/8% Senior Notes Maturing October 2027 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	100.00%
Senior Notes | 5 7/8% Senior Notes Maturing October 2027 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	102.938%
Senior Notes | 5 7/8% Senior Notes Maturing October 2027 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	101.958%
Senior Notes | 5 7/8% Senior Notes Maturing October 2027 | Debt Instrument, Redemption, Period Four
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	100.979%
Senior Notes | 5 7/8% Senior Notes Maturing October 2027 | Debt Instrument, Redemption, Period Five
Debt Instrument, Redemption [Line Items]
Debt instrument, redemption price (percent)	100.00%