Marketable securities (Tables)

12 Months Ended

Dec. 31, 2024

Marketable securities

Schedule of Marketable Securities

			Cost or
			amortized		Unrealized
	Market value		cost		loss, net
	(In millions)
December 31, 2023:
Current assets	$	56.1	$	56.1	$	—
Noncurrent assets	$	4.8	$	5.0	$	(.2)
December 31, 2024:
Current assets	$	1.9	$	1.9	$	—
Noncurrent assets	$	5.7	$	5.7	$	—

Schedule of Marketable Securities and Fair Value Measurements

	Fair Value Measurements
			Quoted		Significant
			Prices in		Other
			Active		Observable
			Markets		Inputs
	Total		(Level 1)		(Level 2)
	(In millions)
December 31, 2023:
Current assets - fixed income securities	$	56.1	$	—	$	56.1
Noncurrent assets:
Fixed income securities	$	2.6	$	—	$	2.6
Mutual funds		2.2		2.2		—
Total	$	4.8	$	2.2	$	2.6
December 31, 2024:
Current assets - fixed income securities	$	1.9	$	—	$	1.9
Noncurrent assets:
Fixed income securities	$	3.1	$	—	$	3.1
Mutual funds		2.6		2.6		—
Total	$	5.7	$	2.6	$	3.1