Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Payments of dividends													$ 13.7	$ 11.7	$ 7.8
Special dividend declared and paid													$ 17.1
Special dividend declared and paid (per share)													$ 0.35
Quarterly dividends paid (in dollars per share)	$ 0.07	$ 0.07	$ 0.07	$ 0.07	$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.04	$ 0.04	$ 0.04	$ 0.04
Kronos
Class Of Stock [Line Items]
Number of shares purchased in market transaction													2,000
NL
Class Of Stock [Line Items]
Common stock awarded to board of directors													15,000	13,750	33,250
Shares available for award	51,150												51,150
NL | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors													200,000
CompX
Class Of Stock [Line Items]
Number of shares available for purchase under repurchase authorizations	523,647												523,647
Shares available for award	131,050												131,050
CompX | Common Class A
Class Of Stock [Line Items]
Number of shares purchased in market transaction													78,900	75,000
Value of of shares purchased in market transaction													$ 1.7	$ 1.3
CompX | Common Class A | Affiliates
Class Of Stock [Line Items]
Number of shares purchased in market transaction													8,900
CompX | Common Class A | Open Market Transaction
Class Of Stock [Line Items]
Number of shares purchased in market transaction													70,000
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	111,800												111,800
Kronos | Maximum
Class Of Stock [Line Items]
Aggregate of common stock awarded to directors													200,000