Other assets - Components (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Other assets:
Note receivables - OPA	$ 84.2	$ 91.6
Pension asset	21.3	19.8
Operating lease right-of-use assets	21.0	20.6
IBNR receivables	15.0	15.0
Land held for development	5.9	7.4
Restricted cash and cash equivalents	5.7	5.5
Other	18.6	21.4
Total	$ 171.7	$ 181.3