Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income taxes
Expected tax expense, at U.S. federal statutory income tax rate of 21%	$ 7,900	$ 3,200	$ 12,500	$ 6,600
Rate differences on equity in earnings of Kronos, net of dividends	(1,500)	(1,200)	(3,400)	(2,200)
U.S. state income taxes and other, net		(100)
Income tax expense	$ 6,435	$ 1,901	$ 9,140	$ 4,406