Marketable Securities - Classification of Marketable Securities (Detail) - USD ($) $ in Millions |
Mar. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Marketable Securities [Line Items] | ||
| Market value | $ 1.8 | $ 3.3 |
| Cost basis | 3.3 | 3.3 |
| Unrealized loss | (1.5) | |
| Level 1 | Common stock | Valhi | ||
| Marketable Securities [Line Items] | ||
| Market value | 1.7 | 3.2 |
| Cost basis | 3.2 | 3.2 |
| Unrealized loss | (1.5) | |
| Level 1 | Common stock | NL And CompX | ||
| Marketable Securities [Line Items] | ||
| Market value | 0.1 | 0.1 |
| Cost basis | $ 0.1 | $ 0.1 |