Revenue recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 192.5	$ 190.6
U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	85.9	93.7
Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	106.6	96.9
Product sales, net
Disaggregation of Revenue [Line Items]
Total revenues	148.2	153.0
Product sales, net | U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	63.9	73.3
Product sales, net | Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	84.3	79.7
Contract development and manufacturing services
Disaggregation of Revenue [Line Items]
Total revenues	21.7	15.9
Contract development and manufacturing services | U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	0.0	0.0
Contract development and manufacturing services | Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	21.7	15.9
Contracts and grants
Disaggregation of Revenue [Line Items]
Total revenues	22.6	21.7
Contracts and grants | U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	22.0	20.4
Contracts and grants | Non-U.S. Government
Disaggregation of Revenue [Line Items]
Total revenues	$ 0.6	$ 1.3