Debt and Credit Facility - Components (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	May 31, 2018
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures	$ (1,177,900)		$ (1,268,700)
Debt issuance cost	(70,900)		(83,600)
Line of Credit
Debt Instrument [Line Items]
Debt issuance cost		$ (1,750)
Senior Notes
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures				$ (10,500)
Debt issuance cost				(24,400)
Senior Notes | 2023 Senior Secured Notes
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures	(3,700)		(4,400)
Debt issuance cost	(8,300)		(10,200)
Senior Notes | 2021 Senior Secured Notes
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures	(2,600)		(3,800)
Debt issuance cost	(5,800)		(8,800)
Senior Subordinated Convertible Debt | 2017 Senior Convertible Debt
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures	(518,900)		(561,900)
Debt issuance cost	(13,400)		(14,500)
Senior Subordinated Convertible Debt | 2015 Senior Convertible Debt
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures	(312,800)		(351,400)
Debt issuance cost	(11,400)		(12,800)
Junior Subordinated Debt | 2017 Junior Convertible Debt
Debt Instrument [Line Items]
Amount of unamortized debt discount of debentures	(339,900)		(347,200)
Debt issuance cost	(3,100)		(3,200)
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Debt issuance cost	(13,600)		(14,700)
Term Loan Facility | Line of Credit
Debt Instrument [Line Items]
Debt issuance cost	$ (15,300)		$ (19,400)	$ (34,700)