Income Taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Expected tax expense, at U.S. federal statutory income tax rate of 21%	$ 2,500	$ 1,200	$ 9,100	$ 1,700
Rate differences on equity in earnings of Kronos, net of dividends	(1,500)	100	(3,700)	(5,300)
U.S. state income taxes and other, net	100	(100)	100
Income tax expense (benefit)	$ 1,054	$ 1,163	$ 5,460	$ (3,616)