Income Taxes - Component of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 35%	$ 3,800	$ (1,100)
Rate differences on equity in earnings (losses) of Kronos	(1,600)	300
Nontaxable income	(200)	(200)
U.S. state income taxes and other, net	200	200
Income tax expense (benefit)	$ 2,179	$ (822)