Stockholder's Equity - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Payments of dividends	$ 0	$ 0	$ 0
NL
Class Of Stock [Line Items]
Common stock awarded to board of directors	28,250	12,600	9,000
Shares available for award	113,150
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	149,050
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	140,900
Kronos | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000