Marketable securities - Schedule of Marketable Securities (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Marketable securities [Line Items]
Market value, current	$ 2.1	$ 56.1
Market value, noncurrent	5.3	4.8
Non Current Assets
Marketable securities [Line Items]
Unrealized loss, net	0.2	(0.2)
Current Assets
Marketable securities [Line Items]
Market value, current	2.1	56.1
Cost or amortized cost	2.1	56.1
Non Current Assets
Marketable securities [Line Items]
Market value, noncurrent	5.3	4.8
Cost or amortized cost	$ 5.1	$ 5.0