Marketable securities - Schedule of Marketable Securities (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Marketable securities [Line Items]
Market value, current	$ 31.7	$ 56.1
Market value, noncurrent	5.5	4.8
Current Assets
Marketable securities [Line Items]
Market value, current	31.7	56.1
Cost or amortized cost	31.7	56.1
Unrealized loss, net	0.0	0.0
Non Current Assets
Marketable securities [Line Items]
Market value, noncurrent	5.5	4.8
Cost or amortized cost	5.5	5.0
Unrealized loss, net	$ 0.0	$ (0.2)