Credit Facilities and Debt - Schedule of Borrowing Obligations (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Nov. 01, 2017	Jun. 21, 2016	Dec. 07, 2015	Jun. 01, 2015	Oct. 22, 2012	Aug. 14, 2012	Oct. 24, 2011
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	310,464
Long-term Debt, Maturities, Repayments of Principal in Year Four	676,488
Long-term Debt, Maturities, Repayments of Principal in Year Five	300,000
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	850,000
Long-term Debt, Gross	2,136,952
Debt Instrument, Unamortized Discount (Premium), Net	(200,546)
Debt Issuance Costs, Noncurrent, Net	(511)	$ (843)
Long-term Debt	1,936,406	2,185,361
Less: current portion	(1,142,870)	0
Long-term Debt, Fair Value	2,143,400	2,423,600
Long-term debt, face value	2,137,000	2,437,000
Long-term portion of debt	793,536	2,185,361
Convertible Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	310,464
Long-term Debt, Maturities, Repayments of Principal in Year Four	676,488
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	350,000
Long-term Debt, Gross	1,336,952
Debt Instrument, Unamortized Discount (Premium), Net	(194,082)
Long-term Debt	1,142,870
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	300,000
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	500,000
Long-term Debt, Gross	800,000
Debt Instrument, Unamortized Discount (Premium), Net	(6,464)
Long-term Debt	793,536
5.375% Senior Notes due August 15, 2020
Debt Instrument [Line Items]
5.375% Senior Notes due 2020	0	298,759					$ 350,000	$ 700,000
Long-term Debt	300,000
2.75% Convertible Debentures due November 1, 2031
Debt Instrument [Line Items]
2.75% Convertible Debentures, net of unamortized discount	46,568	46,568
Long-term debt, face value			$ 46,600		$ 395,500				$ 690,000
Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
2.75% Convertible Debentures, net of unamortized discount	240,406	229,906
Long-term debt, face value						$ 263,900
6.0% Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
5.375% Senior Notes due 2020	298,529	298,220		$ 300,000
Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
5.375% Senior Notes due 2020	$ 580,639	$ 553,973
Long-term debt, face value					$ 676,500