Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Income taxes
Expected tax expense, at U.S. federal statutory income tax rate of 21%	$ 273	$ 1,744
Rate differences on equity in earnings of Kronos, net of dividends	(319)	(782)
U.S. state income taxes and other, net	23	26
Income tax expense (benefit)	$ (23)	$ 988