Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income taxes
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 21%	$ 9,425	$ (62)	$ 13,217	$ (3,088)
Rate differences on equity in earnings (losses) of Kronos, net of dividends	(954)	(1,037)	(2,512)	(3,878)
U.S. state income taxes and other, net	37	134	93	122
Income tax expense (benefit)	$ 8,508	$ (965)	$ 10,798	$ (6,844)