Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Aug. 10, 2020	Mar. 31, 2021
Class A | CompX
Schedule Of Stockholders Equity [Line Items]
Common stock, Repurchased		50,000
Stock repurchase, aggregate purchase price		$ 0.8
Shares available for purchase		600,000
Contran
Schedule Of Stockholders Equity [Line Items]
Non-cumulative dividend on preferred stock	6.00%
Preferred stock returned to contribution agreement authorized designated	5,000
Preferred stock, par value	$ 0.01
Contran | Series A Preferred Stock
Schedule Of Stockholders Equity [Line Items]
Non-cumulative dividend on preferred stock	6.00%
Preferred stock, shares outstanding	5,000