Stockholders' equity - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2022	Sep. 30, 2023
CompX
Class Of Stock [Line Items]
Number of shares available for purchase under repurchase authorizations		523,647
CompX | Common Class A
Class Of Stock [Line Items]
Number of shares purchased in market transaction	78,900
Value of of shares purchased in market transaction	$ 1.7
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
Kronos
Class Of Stock [Line Items]
Number of shares purchased in market transaction	2,000