Stockholder's Equity - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
NL
Class Of Stock [Line Items]
Common stock awarded to board of directors	12,600	9,000	14,000
Shares available for award	141,400
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	156,550
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	149,900
Kronos | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000