Income Taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Expected tax expense, at U.S. federal statutory income tax rate of 35%	$ 8,500	$ 2,500	$ 34,000	$ 2,000
Rate differences on equity in earnings of Kronos	(2,100)	(3,000)	(5,000)	(2,800)
Nontaxable income	(100)	(200)	(300)	(400)
U.S. state income taxes and other, net	200	100	200	100
Income tax expense (benefit)	$ 6,466	$ (560)	$ 28,923	$ (1,052)