Revenue recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 394.7	$ 243.2	$ 587.2	$ 433.9
U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	289.5	132.9	375.4	226.6
Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	105.2	110.3	211.8	207.3
Product sales, net
Disaggregation of Revenue [Line Items]
Total revenues	298.5	183.5	446.7	336.5
Product sales, net | U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	224.2	94.6	288.1	167.9
Product sales, net | Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	74.3	88.9	158.6	168.6
Contract development and manufacturing services
Disaggregation of Revenue [Line Items]
Total revenues	72.6	18.7	94.3	34.6
Contract development and manufacturing services | U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	44.6	0.0	44.6	0.0
Contract development and manufacturing services | Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	28.0	18.7	49.7	34.6
Contracts and grants
Disaggregation of Revenue [Line Items]
Total revenues	23.6	41.0	46.2	62.8
Contracts and grants | U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	20.7	38.3	42.7	58.7
Contracts and grants | Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	$ 2.9	$ 2.7	$ 3.5	$ 4.1