Debt and Credit Facility - Amortization and Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Debt Instrument [Line Items]
Debt issuance amortization	$ 4.2	$ 2.8
Debt discount amortization	29.9	27.7
Other interest expense	0.5	0.4
Total interest expense	132.6	90.4
Senior Secured Indebtedness
Debt Instrument [Line Items]
Debt issuance amortization	3.3	1.9
Debt discount amortization	0.7	0.2
Interest expense	78.7	40.2
Total interest expense on Senior Secured Indebtedness	82.7	42.3
Convertible Debt
Debt Instrument [Line Items]
Debt issuance amortization	0.9	0.9
Debt discount amortization	29.2	27.5
Interest expense	19.3	19.3
Total interest expense on Senior Secured Indebtedness	$ 49.4	$ 47.7
2017 Senior Convertible Debt
Debt Instrument [Line Items]
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)	7 years 7 months 6 days
2015 Senior Convertible Debt
Debt Instrument [Line Items]
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)	5 years 7 months 6 days
2017 Junior Convertible Debt
Debt Instrument [Line Items]
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)	17 years 7 months 6 days