Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income taxes
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 21%	$ 2,048	$ (2,077)	$ 3,792	$ (3,026)
Rate differences on equity in earnings (losses) of Kronos, net of dividends	(776)	(5,146)	(1,558)	(2,841)
U.S. state income taxes and other, net	30	(77)	56	(12)
Income tax expense (benefit)	$ 1,302	$ (7,300)	$ 2,290	$ (5,879)