Income taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income taxes
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 21%	$ 17,497	$ (1,348)	$ 8,241
Nontaxable dividends received from Kronos	(3,550)	(5,621)	(5,621)
U.S. state income taxes and other, net	110	(32)	165
Income tax expense (benefit)	$ 14,057	$ (7,001)	$ 2,785