Debt - Estimated Fair Values of Long-term Debt (Details) - Senior Notes - USD ($) $ in Millions	Dec. 31, 2020	Oct. 29, 2020	Apr. 15, 2020	Dec. 31, 2019	Dec. 31, 2016
6.875% senior secured notes due November 1, 2027
Debt Instrument [Line Items]
Interest rate	6.875%	6.875%
5.50% convertible senior notes due March 1, 2021
Debt Instrument [Line Items]
Interest rate	5.50%				5.50%
10.75% senior secured notes
Debt Instrument [Line Items]
Interest rate	10.75%		10.75%	10.75%
Estimated Fair Value | 6.875% senior secured notes due November 1, 2027
Debt Instrument [Line Items]
Long-term debt	$ 532.3			$ 0.0
Estimated Fair Value | 5.50% convertible senior notes due March 1, 2021
Debt Instrument [Line Items]
Long-term debt	169.8			115.8
Estimated Fair Value | 10.75% senior secured notes
Debt Instrument [Line Items]
Long-term debt	$ 0.0			$ 474.2