Debt - Schedule of Components of Long-term Debt (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Oct. 29, 2020	Dec. 31, 2019	Dec. 31, 2016
Debt Instrument [Line Items]
Finance leases	$ 3,200,000	$ 5,500,000
Other debt	51,900,000	63,900,000
Total	532,900,000	629,900,000
Less – current maturities	18,800,000	102,800,000
Total long-term debt	$ 514,100,000	527,100,000
Senior Notes | Senior Secured Notes Due 2027
Debt Instrument [Line Items]
Interest rate (as a percent)	6.875%		6.875%
Face value	$ 485,000,000.0	485,000,000.0	$ 485,000,000
Unamortized discount and fees	7,200,000	8,100,000
Senior notes	$ 477,800,000	$ 476,900,000
Senior Notes | Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Interest rate (as a percent)	5.50%	5.50%
Face value		$ 84,200,000			$ 213,500,000
Unamortized discount and fees		600,000
Senior notes	$ 0	$ 83,600,000		$ 84,200,000