Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income taxes
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 21%	$ 1,744	$ (949)
Rate differences on equity in earnings (losses) of Kronos, net of dividends	(782)	2,305
U.S. state income taxes and other, net	26	65
Income tax expense (benefit)	$ 988	$ 1,421