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Income Taxes - Component of Income Taxes (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Income Tax Disclosure [Abstract]        
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 35% $ 21,700 $ 600 $ 25,500 $ (500)
Rate differences on equity in earnings (losses) of Kronos (1,300) (100) (2,900) 200
Nontaxable income     (200) (200)
U.S. state income taxes and other, net (100) (200) 100  
Income tax expense (benefit) $ 20,278 $ 330 $ 22,457 $ (492)