Borrowings - Schedule of Long-term Debt (Details) - USD ($)	Sep. 30, 2016	Sep. 30, 2015	Jun. 15, 2006
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 1,331,878,000	$ 1,516,367,000
Debt Instrument, Unamortized Premium	(2,362,000)	3,639,000
Senior Notes
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	1,207,526,000	1,415,332,000
Unamortized debt issuance costs	(14,063,000)	(11,908,000)
Debt Instrument, Unamortized Premium	2,362,000	(3,639,000)
Senior Notes | 8 1/8% Senior Notes Maturing June 2016
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 0	$ 170,879,000
Debt instrument stated interest rate (percent)	8.125%	8.125%
Senior Notes | 6 5/8% Senior Secured Notes Maturing April 2018
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 0	$ 300,000,000
Debt instrument stated interest rate (percent)	6.625%	6.625%
Senior Notes | 9 1/8% Senior Notes Maturing May 2019
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 0	$ 235,000,000
Senior Notes | 5 3/4% Senior Notes Maturing June 2019
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 321,393,000	$ 325,000,000
Debt instrument stated interest rate (percent)	5.75%	5.75%
Senior Notes | 7 1/2% Senior Notes Maturing September 2021
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 198,000,000	$ 200,000,000
Debt instrument stated interest rate (percent)	7.50%	7.50%
Senior Notes | 8 3/4% Senior Notes Maturing March 2022
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 500,000,000	$ 0
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 and debt issuance costs)	$ 199,834,000	$ 200,000,000
Debt instrument stated interest rate (percent)	7.25%	7.25%
Term Loan
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 52,669,000	$ 0
Debt Instrument, Unamortized Discount	$ 880,000	0
Debt instrument stated interest rate (percent)	6.75%
Unamortized debt issuance costs	$ (1,451,000)	0
Junior Subordinated Notes (net of unamortized accretion of $40,903 and $42,970, respectively)
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	59,870,000	57,803,000
Debt Instrument, Unamortized Discount	40,903,000	42,970,000
Debt instrument stated interest rate (percent)			7.987%
Cash Secured Loans
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	0	22,368,000
Other Secured Notes Payable
Debt Instrument [Line Items]
Total debt (net of premium and debt issuance costs)	$ 11,813,000	$ 20,864,000