Components of lease cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Components of lease expense [Line Items]
Finance lease cost, Amortization of right-of-use assets	$ 0.2		$ 0.6
Finance lease cost, Interest on lease liabilities	0.1		0.2
Total finance lease cost	0.3		0.8
Operating lease cost	6.5		19.9
Short-term lease cost	1.4		4.8
Variable lease cost	2.5		6.7
Total lease cost	10.7		32.2
Cost of Sales [Member]
Components of lease expense [Line Items]
Lease expense	8.0	$ 7.1	24.0	$ 21.4
Selling, General and Administrative Expenses [Member]
Components of lease expense [Line Items]
Lease expense	$ 2.4	$ 2.4	$ 7.4	$ 7.4