Stockholder's Equity - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
NL
Class Of Stock [Line Items]
Common stock awarded to board of directors	9,000	14,000	9,000
Shares available for award	154,000
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	166,000
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	155,500
Kronos | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000