Income Taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 35% in 2017 and 21% in 2018	$ (4,400)	$ 8,500	$ (12,100)	$ 34,000
Rate differences on equity in earnings of Kronos	(1,900)	(2,100)	(4,300)	(5,000)
Nontaxable income		(100)	(200)	(300)
U.S. state income taxes and other, net	200	200	1,200	200
Income tax expense (benefit)	$ (6,158)	$ 6,466	$ (15,416)	$ 28,923