Debt - Schedule of Interest Expense (Details) - Senior Notes - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
2022 Notes
Debt Instrument [Line Items]
Contractual interest coupon	$ 47.3	$ 47.3	$ 33.2
Amortization of debt discount	2.4	2.4	1.7
Total	49.7	49.7	34.9
2021 Notes
Debt Instrument [Line Items]
Contractual interest coupon	8.9	11.8	11.8
Amortization of debt discount	5.5	6.6	6.0
Amortization of debt issuance costs	0.9	1.2	1.2
Total	$ 15.3	$ 19.6	$ 19.0