Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income taxes
Expected tax expense, at U.S. federal statutory income tax rate of 21%	$ (949)	$ 4,602
Rate differences on equity in earnings of Kronos, net of dividends	2,305	(1,914)
U.S. state income taxes and other, net	65	17
Income tax expense	$ 1,421	$ 2,705