Income Taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 35%	$ 39,300	$ 4,900	$ (18,000)
Rate differences on equity in earnings (losses) of Kronos	(7,400)	(7,400)	(7,400)
Adjustment to the reserve for uncertain tax positions, net			(3,000)
Change in federal tax rate, net	(37,500)
U.S. state income taxes and other, net		(300)	(200)
Income tax benefit	$ (5,634)	$ (2,777)	$ (28,611)