Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Carrying Amount | 2023 Senior Secured Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	$ 985.4
Carrying Amount | 2021 Senior Secured Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	987.4
Carrying Amount | Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	1,892.1
Carrying Amount | 2017 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	1,493.6	$ 1,437.6
Carrying Amount | 2015 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	1,360.8	1,309.9
Carrying Amount | 2017 Junior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	335.9	326.7
Fair Value | 2023 Senior Secured Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	1,020.1
Fair Value | 2021 Senior Secured Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	1,008.1
Fair Value | Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	1,911.5
Fair Value | 2017 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	2,285.4	2,459.2
Fair Value | 2015 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	2,810.6	3,079.1
Fair Value | 2017 Junior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for subordinated convertible debentures	$ 740.8	$ 876.9