Leases - Supplemental balance sheet information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases
Weighted-average remaining lease term of operating leases	4 years 7 months 6 days	4 years 9 months 18 days
Weighted-average remaining lease term of finance leases	3 years 2 months 12 days	3 years 8 months 12 days
Weighted-average discount rate for operating leases	13.10%	11.90%
Weighted-average discount rate for finance leases	12.40%	10.70%
Interest on financing lease liabilities	$ 2.3	$ 2.6
Amortization expense on finance lease right-of-use assets	$ 9.1	$ 12.8