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 |