Income Taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 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 and 2019		$ 6,000	$ (11,400)	$ 39,300
Rate differences on equity in earnings of Kronos		(5,300)	(5,000)	(7,400)
Change in federal tax rate, net	$ (37,500)		800	(37,500)
U.S. state income taxes and other, net		(100)	200
Income tax expense (benefit)		$ 579	$ (15,361)	$ (5,634)