Debt - Schedule of Interest Expense (Details) - Senior Notes - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
The Notes
Debt Instrument [Line Items]
Contractual interest coupon	$ 2.0	$ 11.8	$ 13.8	$ 23.6
Amortization of debt issuance costs	0.1	0.6	0.7	1.2
Total	2.1	12.4	14.5	24.8
2021 Notes
Debt Instrument [Line Items]
Contractual interest coupon	1.1	2.9	2.3	5.9
Amortization of debt discount	0.8	1.8	1.6	3.5
Amortization of debt issuance costs	0.1	0.3	0.2	0.6
Total	$ 2.0	$ 5.0	$ 4.1	$ 10.0