Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Class Of Stock [Line Items]
Quarterly dividends paid (in dollars per share)	$ 0.09	$ 0.08	$ 0.07
Payments of dividends	$ 17.6	$ 15.6	$ 13.7
Special dividend declared and paid	$ 10.3	$ 21.0
Special dividend declared and paid (per share)	$ 0.21	$ 0.43
NL
Class Of Stock [Line Items]
Common stock awarded to board of directors	15,000	14,250	17,750
Shares available for award	170,750
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	115,150
CompX | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000		200,000
Kronos
Class Of Stock [Line Items]
Shares available for award	71,000
Kronos | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors	200,000