Intangible assets - Schedule of Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Cost
Intangible assets, gross	$ 822.1	$ 822.1
Finite-lived intangible assets acquired	10.0
Finite-lived intangible assets, accumulated amortization	124.0	109.2
Intangible assets, net	$ 708.1	$ 712.9
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period of intangible asset	9 years	9 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period of intangible asset	22 years	22 years
Products
Cost
Intangible assets, gross	$ 788.0	$ 788.0
Finite-lived intangible assets acquired	10.0
Finite-lived intangible assets, accumulated amortization	96.0	82.2
Intangible assets, net	$ 702.0	$ 705.8
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Amortization period of intangible asset	8 years	8 years
Cost
Intangible assets, gross	$ 28.6	$ 28.6
Finite-lived intangible assets, accumulated amortization	23.8	23.0
Intangible assets, net	$ 4.8	$ 5.6
Contract development and manufacturing services
Finite-Lived Intangible Assets [Line Items]
Amortization period of intangible asset	8 years	8 years
Cost
Intangible assets, gross	$ 5.5	$ 5.5
Finite-lived intangible assets, accumulated amortization	4.2	4.0
Intangible assets, net	$ 1.3	$ 1.5