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Stockholder's Equity - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Payments of dividends	$ 7,800,000	$ 0	$ 0
Quaterly dividends payable, amount per share	$ 0.04
NL
Class Of Stock [Line Items]
Common stock awarded to board of directors	33,250	28,250	12,600
Shares available for award	79,900
NL | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000
CompX
Class Of Stock [Line Items]
Shares available for award	140,950
CompX | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000
Kronos
Class Of Stock [Line Items]
Shares available for award	127,400
Kronos | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000

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