Segment information - Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information
Assets	$ 2,469.0	$ 2,334.5
Operating Segments
Segment Reporting Information
Assets	2,404.0	2,285.4
Operating Segments | Performance Materials
Segment Reporting Information
Assets	473.6	751.4
Operating Segments | Performance Chemicals
Segment Reporting Information
Assets	1,930.4	1,534.0
Corporate and other
Segment Reporting Information
Assets	$ 65.0	$ 49.1