Other Assets - Other Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Other noncurrent assets:
Land held for development	$ 59.7	$ 96.0
Operating lease right-of-use assets	21.8	26.1
Restricted cash and cash equivalents	37.6	37.8
IBNR receivables	32.6	37.1
Marketable securities	3.5	2.9
Pension asset	10.0	8.4
Note receivables - OPA	29.0	25.3
Other	13.5	8.7
Total	$ 207.7	$ 242.3