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Marketable Securities - Classification of Marketable Securities (Detail) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]    
Market value $ 6.0 $ 2.4
Cost basis 3.3 3.3
Unrealized gain (loss) 2.7 (0.9)
Level 1 | Common stock | Valhi    
Schedule Of Available For Sale Securities [Line Items]    
Market value 5.9 2.3
Cost basis 3.2 3.2
Unrealized gain (loss) 2.7 (0.9)
Level 1 | Common stock | NL And CompX    
Schedule Of Available For Sale Securities [Line Items]    
Market value 0.1 0.1
Cost basis $ 0.1 $ 0.1