Borrowings - Schedule of Long-term Debt (Details) - USD ($)	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 15, 2006
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 1,327,412,000		$ 1,331,878,000
Debt Instrument, Unamortized Premium	$ (3,413,000)		$ (2,362,000)
5 3/4% Senior Notes Maturing June 2019
Debt Instrument [Line Items]
Debt instrument stated interest rate (percent)	5.75%		5.75%
7 1/2% Senior Notes Maturing September 2021
Debt Instrument [Line Items]
Debt instrument stated interest rate (percent)	7.50%		7.50%
8 3/4% Senior Notes Maturing March 2022
Debt Instrument [Line Items]
Debt instrument stated interest rate (percent)	8.75%		8.75%
7 1/4% Senior Notes Maturing February 2023
Debt Instrument [Line Items]
Debt instrument stated interest rate (percent)	7.25%		7.25%
6 3/4% Senior Notes Maturing March of 2025
Debt Instrument [Line Items]
Debt instrument stated interest rate (percent)	6.75%
Senior Notes
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 1,259,840,000		$ 1,207,526,000
Unamortized debt issuance costs	(14,800,000)		(14,063,000)
Debt Instrument, Unamortized Premium	3,413,000		2,362,000
Senior Notes | 5 3/4% Senior Notes Maturing June 2019
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 321,393,000		321,393,000
Debt instrument stated interest rate (percent)	5.75%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 0		198,000,000
Debt instrument stated interest rate (percent)	7.50%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 500,000,000		500,000,000
Debt instrument stated interest rate (percent)	8.75%
Senior Notes | 7 1/4% Senior Notes Maturing February 2023
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 199,834,000		199,834,000
Debt instrument stated interest rate (percent)	7.25%
Senior Notes | 6 3/4% Senior Notes Maturing March of 2025
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 250,000,000		0
Debt instrument stated interest rate (percent)		6.75%
Term Loan
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	0		52,669,000
Debt Instrument, Unamortized Discount	0		880,000
Unamortized debt issuance costs	0		(1,451,000)
Junior Subordinated Notes (net of unamortized accretion of $38,837 and $40,903, respectively)
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	61,937,000		59,870,000
Debt Instrument, Unamortized Discount	38,837,000		40,903,000
Debt instrument stated interest rate (percent)				7.987%
Other Secured Notes Payable
Debt Instrument [Line Items]
Total debt (net of premium/discount and debt issuance costs)	$ 5,635,000		$ 11,813,000